Judy LaRosa-Thompson Choon-Keun Park, PQ Corporation Sangyong Research Center
Michael Silsbee, Pennsylvania State Univ
- Federal Highway Administration
- Hanil Cement Manufacturing Company Ltd.
- National Science Foundation
- Portland Cement Association
- Ssangyong Cement Ind. Ltd.
* Invited paper
SESSION MM1: WASTE TREATMENT AND UTILIZATION
Chair: Gregory J. McCarthy
Monday Morning, December 1, 1997
Independence West (S)
8:30 AM MM1.1
DIAGENESIS OF HIGH-SODIUM LIGNITE COMBUSTION BYPRODUCTS. Gregory J. McCarthy, Dean G. Grier, North Dakota State University, Department of Chemistry, Fargo, ND; Ray D. Butler, High Plains Consortium, Inc., Bismarck, ND.
High-calcium fly ash and dry flue gas desulfurization (FGD) residues are usually cementitious. Core samples of FGD residues (scrubber ash and bottom ash) derived from high-sodium North Dakota lignite disposed for more than ten years have been studied by XRD and SEM/EDS. The original conditioned scrubber ash assemblage included: typical lignite fly ash phases (quartz, periclase, merwinite, melilite, ferrite spinel, and anhydrite) and sodium sulfates; lime and portlandite (unreacted sorbent); and hannebachite, bassanite, and gypsum (scrubber phases). Bottom ashes typically included pyroxene, melilite, merwinite, quartz, ferrite spinel, and nepheline. Both materials also contained significant noncrystalline Na-Ca-aluminosilicate glass. During long term burial, the disposed dry scrubber ash and bottom ash underwent transformations from the original mineral assemblages through processes analogous to natural diagenesis. Eight core samples were studied. Several showed assemblages typical of hydrated dry scrubber residues: ettringite and thaumasite; unreacted fly ash and scrubber residue phases; and noncrystalline material. A second type of assemblage was found to consist almost entirely of an ettringite-thaumasite solid solution, with minor amounts of non-reactive fly ash phases and glass. A third type of assemblage contained tobermorite and a number of high-sodium phases: Na-P1 zeolite, hauyne-nosean, and sodium-calcium-sulfate-hydrate. Both ettringite and thaumasite were absent in this third assemblage. To our knowledge, formation of tobermorite in coal combustion byproducts and related materials under natural ambient conditions has not previously been reported.
8:45 AM MM1.2
PROPERTIES OF BLAST-FURNACE SLAGS CONTAINING HIGH AMOUNTS OF MANGANESE. Jean Pera, Jean Ambroise, and Lionel Coutaz, U.R.G.C. Materiaux, Institut national des Sciences Appliquees de Lyon, Villeurbanne, FRANCE.
This paper presents tests results carried out to characterize the physical and chemical properties of 4 blast furnace slags containing from 4 to 16% of manganese. The interactions between ordinary portland cement or calcium hydroxide and each slag were investigated by means of X-ray diffraction, scanning electron microscopy, thermoanalysis, and conductimetry. Mortars and concretes using these slags were cast. When ground to a Blaine surface area of 300 m2/kg, the slags were utilized in road binders in combination with calcium hydroxide or portland cement. When ground to a Blaine surface area of 600 m2/kg, the slags were introduced in the composition of self-leveling concretes and high strength concretes.
9:00 AM MM1.3
PORE SOLUTION CHEMISTRY OF GROUND GRANULATED BLAST-FURNACE SLAG. Sujin Song, Dept of Materials Science and Engineering, Northwestern University, Evanston, IL; Hamlin Jennings, Dept of Materials Science and Engineering, Dept of Civil Engineering, Northwestern University, Evanston, IL.
The hydration of ground granulated blast-furnace slag (GGBFS) pastes in various pH-environment was investigated. The chemical composition and pH of the pore solutions extracted from six different GGBFS pastes have been determined. The concentrations of Si, Ca, Al, and Mg are functions of the pH of the aqueous phase with high pH associated with the higher concentrations of Si and Al, and the lower concentrations of Ca and Mg. The relationship between pH and ionic concentration of those species could be explained using the equilibrium solubility product. A starting aqueous phase with pH higher than 11.5 seems to be an effective activator. The main hydration product was identified as C-S-H and hydrotalcite was observed in the pastes with aqueous phase of high pH at later stages of hydration. The effect of pore solution on the alkali-activation of GGBFS is also discussed with reference to the formation of hydrotalcite.
9:15 AM MM1.4
THE ADSORPTION OF SO2 BY ZEOLITES SYNTHESIZED FROM FLY ASH. Anand Srinivasan and Michael Grutzek, Intercollege Materials Research Laboratory, The Pennsylvania State University, University Park, PA.
A number of zeolites were synthesized from a series of Class F fly ashes using sodium hydroxide solutions and autogenous conditions at 85-150C. The zeolites were characterized and then dried at 150C. At this point they were used to adsorb sulphur dioxide (SO2) from a simulated stack gas containing 2000 ppm S02. Results suggest that a utility could conceivably synthesize its own zeolites on site and then use them in a fixed bed configuration to meet standard SO2 emission requirements. If successful, this technology may provide an attractive alternative to wet scrubbing with lime based materials.
9:30 AM MM1.5
SULFO ALUMINATE CEMENT FROM LOW CALCIUM FLY ASH AND SULFUR RICH INDUSTRIAL WASTE. P. Arjunan, M.R. Silsbee and D.M. Roy, Materials Research Laboratory, The Pennsylvania State University, University Park, PA.
Production of Portland cement poses two major problems, a) consumption of large amounts of calcium rich raw materials and b) consumption of large quantities of high quality energy. Substitution of calcium rich compounds with lower calcium content compounds will help eliminate these two major problems. The main objective of this study is the preparation and characterization of environmentally friendly cements with performance characteristics similar to those of Portland cement, from industrial wastes like bag house dust, low calcium fly ash and scrubber sludge. Promising preliminary results show the formation of low temperature phases calcium sulfo aluminate(4CaO.3Al2O3.SO3) and dicalcium silicate(2CaO. SiO2) at around 1175C as compared to the 1500C sintering temperature required for Portland cement. Phases of the developed cements were predicted using modified bogue calculation and computational technique. Excellent correspondence were observed between the predicted and real phase compositions. Isothermal calorimetric measurements indicate the good hydration properties of the developed cement comparable to ordinary Portland cement. Mechanical properties and micro structural evaluations confirm the usefulness of this new cement.
10:15 AM *MM1.6
WASTE TREATMENT USING CEMENT. F.P. Glasser, University of Aberdeen, Aberdeen, SCOTLAND.
Several decades of experience have accumulated on the use of alkaline cements to provide physical containment, as well as chemical conditioning, for a range of toxic and radioactive wastes. The material science of cement underlies the effectiveness of these processes. Yet it is concluded that material properties have not always been used appropriately in the design of systems, nor have they been applied to product testing and to predicting long term performance.
The presentation emphasises (i) the underlying science behind leach testing: a new iso-pH test in which leachant pH is controlled by bubbling CO2 is described and (ii) developments in long term property prediction which couple aqueous solution chemistry at elevated pH to standard geochemical speciation codes, to assess chemical and mineralogical changes. Good agreement is obtained between calculated and experimental results where the underlying data base are sufficiently robust to support calculation. Data needs are outlined. Efforts to correlate and corroborate models, with the results from leach tests and actual field exposure - now underway in a co-operative programme supported by the Commission of the European Communities - are described.
10:45 AM MM1.7
UTILZATION OF DRY FLUE GAS DESULFURIZATION (dfGD) FLY ASH IN BLENDED EXPANSIVE CEMENT. Stephen Kwan, Praxis Engineers, Milpitas, CA.
Dry Flue Gas Desulfurization (dFGD) fly ash has been used to produce a blended expansive cement. Compared to current commercial expansive cement, the dFGD blended cement is lower cost and has favorable properties including higher compressive strength and lower permeability while passing all relevant ASTM standards for expansive mortar and concrete.
11:00 AM MM1.8
WORKABILITY ASSESSMENT FOR POLYSTYRENE AGGREGATE CONCRETE. Ben Sabaa, Rasiah Sri Ravindrarajah, Faculty of Engineering, University of Technology, Sydney, AUSTRALIA.
The standard workability tests for concrete mixtures measure one or more of the characteristics of fresh concrete. No single test can be used to cover the degrees of workability from very low to very high. The existing standard tests are commonly used to determine the workability of lightweight concrete. although experience is needed to interpret the results. Workability of polystyrene aggregate concrete is affected by unit weight and mix compositions. This paper, which forms a part of an extensive study of the properties of polystyrene aggregate concrete, discusses the applicability of the standard tests such as slump, vebe, compacting factor and DIN compaction index for polystyrene aggregate concrete. The polystyrene aggregate concrete mixtures, having the unit weight between 1600 and 2000 kg/m3 were produced by partially replacing the coarse aggregate of a normal weight concrete mixture with expanded polystyrene aggregate. By varying the water content from 180 to 270 kg/m3, polystyrene aggregate concrete mixtures, various degrees of workability were achieved. The concrete mixtures were subjected to visual inspection, involving touching, patting and trowelling, for the assessment of wetness, mobility, compactability, plasticity, and cohesiveness. The polystyrene aggregate concrete had a reduced slump compared to normal weight concrete having the same degree of workability. Vebe and compacting factor tests failed to show any clear relationship between the measured values and the unit weight of concrete. DIN compaction index test was judged to be the most suitable workability test for polystyrene aggregate concrete having a wide range of workability. The compaction index values for polystyrene aggregate concrete mixes having low, medium and high degree of workability are 1.30 or more, 1.15 to 1.29, and 1.04 to 1.14, respectively; while the slump values are 10 mm or less, 10 to 40 mm, and more than 40 mm, respectively. The relationships among slump, vebe, compacting factor and compaction index are also presented.
11:15 AM MM1.9
ENGINEERING PROPERTIES OF LIGHTWEIGHT CONCRETE CONTAINING CRUSHED EXPANDED POLYSTYRENE WASTE. Ben Sabaa, Rasiah Sri Ravindrarajah, Faculty of Engineering, University of Technology, Sydney, AUSTRALIA.
Crushed waste expanded polystyrene is used in combination with the normal weight aggregates to produce lightweight concrete. The density of the concrete is varied between 1600 to 2000 kg/m3. The cement contents of polystyrene aggregate concrete were 410 and 540 kg/m3. This paper reports the results of an experimental investigation into the effects of paste content and density on the strength and deformational properties of polystyrene aggregate concrete. A comparison is made for the properties of polystyrene aggregate concrete with those for the lightweight aggregate concrete. The experimental results showed that the polystyrene aggregate concrete have a higher modulus of elasticity for a given strength than expanded shale, clay or slate lightweight aggregate concrete. The creep of polystyrene aggregate concrete increased with the decrease in the density of concrete. However, the density of concrete influences the strength of concrete more significantly than its creep potential. The 150-day creep coefficient for polystyrene concrete in the density range of 1600 to 2000 kg/m3, subjected to a stress/strength ratio of 0.30 and loaded at 28 days, was between 1.43 and 2.07 for the concrete with the cement content of 410 kg/m3. With the cement content of 540 kg/m3, the creep coefficient ranged between 1.55 and 1.89. Polystyrene aggregate concrete that show increased shrinkage also exhibited higher creep.
SESSION MM2: COMPOSITE AND REINFORCED CONCRETE
Chair: Tahar El-Korchi
Monday Afternoon, December 1, 1997
Independence West (S)
1:30 PM MM2.1
CARBON FIBER REINFORCED CONCRETE FOR CORROSION CONTROL. Jiangyuan Hou and D.D.L. Chung, Composite Materials Research Laboratory, State University of New York at Buffalo, Buffalo, NY.
Carbon fiber reinforced concrete is attractive in three ways for corrosion control of embedded steel rebars. Firstly, due to thesilica fume or latex in carbon fiber reinforced concrete, this concrete provides more corrosion resistance to embedded steel rebars than plain concrete. Carbon fibers themselves decrease the corrosion resistance due to decrease in electrical resistivity,up but the negative effect is more than made up for by adding either silica fume or latex, which decreases the water absorptivity. Latex helps also because it increases the resistivity. Secondly, due to its low resistivity, concrete containing carbon fibers and silica fume reduces by 18% the driving voltage required for cathodic protection of embedded steel rebars compared to plain concrete, and by 28% compared to concrete with silica fume. Thirdly, due to its low resistivity, mortar containing carbon fibers and latex, and used as an overlay to embed titanium wires for electrical contacts to steel reinforced concrete for cathodic protection, reduces by 10% the driving voltage required for cathodic protection, compared to plain mortar overlay. In spite of the low resistivity of mortar overlay with carbon fibers, cathodic protection requires multiple metal electrical contacts embedded in the mortar at a spacing of 11 cm or less.
1:45 PM MM2.2
FABRICATION AND MECHANICAL PROPERTIES OF FIBER REINFORCED LIGHTWEIGHT CEMENT COMPOSITES. Seung Bum Park, Dept of Civil Engineering, Chungnam National University, Taejon, KOREA; Eui Sik Yoon, Dept of Structural Systems & Site Evaluation, Korea Institute of Nuclear Safety, Taejon, KOREA; Burtrand I. Lee, Dept of Ceramic and Materials Engineering, Clemson University, Clemson, SC.
Low density/low cost cement composites were fabricated. Fibers of carbon, alkali resistant glass, polypropylene, and vinylon were considered to reinforce the matrix of industrial by-products; silica fume and fly ash with portland cement, calcium silicates and lightweight additives under various mixing conditions and proportions. The results of an experimental study on fabrication and mechanical properties of light weight cement composites are presented. The low density was obtained by adding aluminum powder foaming agent and autoclave curing of the composites. Under the high alkali/autoclaving conditions, only the carbon fibers and glass fibers could withstand the alkali, heat and pressure to be effective in reinforcing the matrices. Carbon fibers and alkali resistant glass fibers were effective in reinforcing the matrices but carbon fibers were superior to glass fibers. A remarkable increase in fracture energy was observed by the addition of carbon fibers. In fly ash/cement composites the workability was improved by the increasing ratio of fly ash to cement with reduction in bulk density, compressive and flexural strengths. The flexural and compressive strengths were higher for the composites cured in hot water as compared with composites cured in a humid air. Fabrication techniques for producing lightweight fly ash/cement composites replaceable of autoclaved lightweight concrete is developed. The optimum fabrication conditions for producing lightweight fly ash/cement composites are proposed.
2:00 PM MM2.3
FIBER-REINFORCED CEMENT COMPOSITES. Vladimir Serbin, Tatyana Serbina, National Technical Univ of Ukraine, Dept of Chemical Technology, Kiev, UKRAINE.
Association of high-strength fibres with help of a suitable matrix allows to receive a composite material the strength of which in a direction of fibres at a stretching in a general case is defined by their strength and volumetric contents. Besides it, the number of the factors are influences on the strength of a composite and provides effective joint work of components yet. Composites with a matrix from various cements and mineral fibres from synthetic glasses, known under the general name glasscement, are considered in the present message. Also is proposed method of forecasting of durability fiber-reinforced cement composites taking into account stability of a fibre in environment of hardening cement stone and stability of physic-mechanical properties of a composition as a whole. In cement matrix the mineral fibre is under influence of a complex of physic- chemical and physic-mechanical processes, determining the stability of properties of system in time. Thus occurs: - interaction the environment of hardening binder with a fibre; - crystallizing and overcrystallizing processes connected with formation of the structure of a matrix; - deformation of a matrix, caused of it shrinkage or expansion, developing in a composite under various influences. Modern building industry demand from materials and products, besides profitability , yet the number of special requirements. Application of fibre- reinforced cement composites allows to lower the cost of construction at the expense of reduction the weight of a product, decrease the transport charges and damage of products, reduction the thickness of walls at preservation of required resistance of heat transfer, facilitation of a skeleton, reduction the expenses by installation and fire-preservation measures, etc.
2:15 PM MM2.4
FREE SHRINKAGE MODEL OF STEEL FIBER REINFORCED CONCRETE. Fang Fang, Balendran, R.V., C.M. Tam, Dept. of Building and Construction, City University of Hong Kong, HONG KONG.
This paper proposes an empirical model for predicting the progress of long term free shrinkage strain of steel fibre reinforced concrete from relatively short term shrinkage tests. On the basis of free shrinkage models of ordinary concrete, the major parameters concerned are compressive strength and the characteristics of fibre including the fibre volume ratio, fibre length and fibre diameter. The model is verified by the test results on shrinkage strain of melt extract, crimped and hooked steel fibber reinforced concrete presented by Azari (1984). By plotting the experiment data against t(age of concrete, days) to have a regression analysis, a best fit straight line is being established to determine the constants. The coefficient of variation of the constants Œ¹a¹¹ and Œ¹b¹¹ of hooked, melt-extract and crimped steel fibre concrete are about 6%, 6% and 9%, respectively. These results show that the predicted shrinkage strain-time curve is in good agreement with the experimental data.
2:30 PM MM2.5
NEW APPROACH FOR TENSILE TESTING OF FRP COMPOSITES. Tahar El-Korchi1, Houssam A. Toutanji2, Shuji Tsubota3, 1Worcester Polytechnic Institute, Worcester, MA; 2University of Alabama in Huntsville, Huntsville, AL; 3Worcester Polytechnic Institute, Worcester, MA.
The use of fiber reinforced plastic (FRP) composite wrap is increasingly being used for repair and rehabilitation of concrete structures. The tensile strength is one of the most important mechanical properties of these composites. A new testing approach using the ASCERA hydraulic tensile tester is introduced and test results presented. This testing technique provides a more uniform stress distribution throughout the specimen, thus, minimizes eccentricity and gripping effects. In this paper, the tensile strength data of: 1) FRP sheets without resin system, 2) FRP tow sheets embedded in epoxy resin-matrix, and 3) cement-based composites wrapped with FRP tow sheets, are presented and discussed. Three types of sheets, including two carbon fiber composites and one glass fiber composite, were applied with a two-part epoxy resin system. The tensile strength values obtained by using the ASCERA machine were compared to those tested by the traditional uniaxial tensile testing technique and published manufacturer data. A comparison between the strength and stiffness of fiber sheets with and without resin system was made. Tensile strength values of the carbon fiber wrapped cement composites were in the range of 78 to 132 MPa. The glass fiber wrapped composites were in the range of 40 to 55 MPa. The tensile strength of the unwrapped cement-based specimens were under 7 MPa. These results show that there are significant differences in the mechanical properties of Elber specimens with and those without the epoxy-resin system. The strength values of cement-based fiber wrapped specimens were presented using Weibull statistics. The rule of mixtures model was used to predict the tensile strength of the FRP composite. Fractography was used to identify the failure initiating flaw and failure mode for the fractured tensile specimens. Failure modes appear distinct for different cement-composite wrap systems.
2:45 PM MM2.6
PERFORMANCE OF CONCRETE COLUMNS STRENGTHENED WITH ADVANCED COMPOSITES AT LOW TEMPERATURE. Houssam A. Toutaji, Department of Civil and Environmental Engineering, University of Alabama in Huntsville, Huntsville, AL; Francisco Rey, Department of Civil Engineering, University of Puerto Rico, Mayagüez, PR.
This paper presents the results of an experimental study on the performance of concrete columns wrapped with carbon and glass fiber reinforced plastic (FRP) composite sheets subjected to freeze-thaw conditions. Concrete columns, measuring 3x12 in, were wrapped with three different types of FRP sheets: two carbon and one glass. Test variables included the type of fiber (C1, C5, and GE) and the environmental exposure conditions. The specimens were conditioned in two different environments: room temperature (+20C) and 300 freeze/thaw cycles. The stress-strain behavior in compression of the freeze/thaw exposed specimens was obtained in order to evaluate their strength, stiffness, and ductility, which were then compared to the performance of unconditioned samples (room temperature). The failure of the wraps of the freeze/thaw exposed specimens started at the top of the cylinder, whereas in the unexposed specimens, the failure initiated from one-fourth to midway along the height of the column. Results show that both CFRP and GFRP wrapped specimens experienced significant reductions in strength and ductility due to freeze/thaw cycling. The reduction in strength ranged between 19 and 28% depending upon the type of fiber. The tested freeze/thaw specimens were cut at 3 in. from the top and at 3 in. from the bottom, taking off the failed portions of the specimen where the surface of the concrete column was directly exposed to freeze/thaw cycles. The shortened specimens were retested again in compression. Results show that strength values obtained from the retested specimens (specimens measuring 3x6 in) were significantly higher than those tested the first time, even with the collection for height/diameter ratio. This indicates that the reduction of strength was due to both the degradation of the FRP composites and the damaged concrete that was subjected to the harsh condition of freezing and thawing.
3:00 PM MM2.7
IMPROVING BOND STRENGTH BETWEEN CONCRETE AND STEEL REBAR. Xuli Fu and D.D.L. Chung, Composite Materials Research Laboratory, State University of New York at Buffalo, Buffalo, NY.
The bond between concrete and steel rebar was evaluated by electromechanical pull-out testing (measuring both shear bond strength and contact electrical resistivity). The bond strength was increased by rebar surface treatment, polymer addition to concrete, increase in water/cement ratio and decrease in curint age of concrete. Rebar surface treatment involving ozone was more effective than those involving water and sand blasting, which were in turn more effeetive than acetone treatment. Ozone and water treatments worked because of the formation of an oxide film on the rebar surface. Sand blasting worked because of surface roughening. Latex addition (20% by weight of cement) to concrete was as effective as ozone treatment of rebar in increasing the bond strength; it worked because of the formation of a polymer interface layer. Methylcellulose (0.4% by weight of cement) was only slightly less effective than latex. Increase of the water/cement ratio increased the bond strength, due to improved fluidity of concrete mix and the consequent slight decrease in the interfacial void content. Increase of the curing age of the concrete decreased the bond strength, due to driving shrinkage of concrete and the consequent increase in the interfacial void content.
3:15 PM MM2.8
FLEXURAL MODELING OF CELLULOSE FIBER REINFORCED THIN SHEET CEMENT COMPOSITES. Patricia J. Kim, Hwai-Chung Wu, Zhong Lin, Victor C. Li, Benoit de LHoneux* and Stephen A.S. Akers**; Advanced Civil Engineering Materials Research Laboratory, Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI; * Redco N.V., Kapelle-op-den-Bos, BELGIUM; ** Eternit AG, Niederurnen, SWITZERLAND.
Flexural modeling of refined (150 CSF) and unrefined (700 CSF) cellulose fiber reinforced thin sheet cement composites (CFRCC) using a modified version of the Cox model provides estimates of the cellulose fiber interfacial microparameters under dry, wet, and accelerated aged (carbonation) conditions while accurately predicting the mode of cellulose fiber failure, fracture or pull-out. The flexural model provides an analytical tool for relating environmental effect on interface and matrix properties to composite properties. This tool is useful for the study of composite durability. Alteration of the cellulose interfacial chemical bond (Go,) frictional bond (to), and snubbing coefficient (f) in modeling with only minor changes to the cellulose fiber properties accounts for the trends in experimental CFRCC mechanical properties for the dry, wet, and aged environments, which are unaffected by the level of cellulose refinement. Limit of proportionality (LOP) aged is greater than LOP dry, which in turn is greater than LOP wet. Modulus of rupture (MOR) aged is greater than MOR dry, which in turn is greater than MOR wet. Composite toughness (IMOR) aged is less than IMOR dry, which in turn is less than IMOR wet. For dry refined CFRCC, chemical bond of the cellulose fibers to the cement matrix is estimated to be a moderate 3.0 J/m2, frictional bond 0.8 MPa, and snubbing coefficient 0.8. For wet CFRCC, chemical bond decreases to 1.0 J/m2, frictional bond remains 0.8 MPa, and snubbing coefficient drops to 0.5. For aged CFRCC, chemical bond increases to 3.5 J/m2, frictional bond increases to 3.0 MPa, and snubbing coefficient 0.8. For unrefined CFRCC, frictional bond and snubbing coefficient slightly decrease when compared to refined CFRCC; chemical bond stays unchanged.
SESSION MM3: IN-ROOM POSTER SESSION
Chairs: Della M. Roy and J. Francis Young
Monday Afternoon, December 1, 1997
Independence West (S)
DURABILITY PERFORMANCE OF CEMENT-BASED MATERIALS WRAPPED WITH FRPC SHEETS. Houssam A. Toutanji, Department of Civil and Environmental Engineering, University of Alabama in Huntsville, Huntsville, AL; Tahar El-Korchi, Department of Civil and Environmental Engineering, Worcester Polytechnic Institute, Worcester, MA.
Fiber reinforced plastic composite (FRPC) wrap has been established as an effective method for rehabilitation and strengthening of concrete structures. This paper presents the results of an experimental study on the tensile performance of cement and concrete materials wrapped with FRPC sheets subjected to wet-dry and freeze-thaw cycles. The tensile test was conducted using the ASCERA hydraulic tensile tester. This test technique provides a more uniform tensile loading and minimizes gripping stresses and misalignment which can be a significant source of error. Three types of fiber composite wraps including two carbon fibers and one glass fiber were applied with two-part epoxy resin matrix. Test variables included the type of fiber (C1, C5, and GE) and the environmental exposure conditions. The specimens were conditioned in three different environments, as follows: a) room temperature (+20C), b) 300 wet/dry cycles using salt water, and c) 300 freeze/thaw cycles. At the end of each exposure, tensile strength behavior in tension was obtained and then compared to the performance of unconditioned samples. Test results show that the CFRP wrapped specimens experienced no reduction in strength due to wet/dry or freeze/thaw exposure, whereas the GFRP wrapped specimens experienced a significant reduction in strength. The glass fiber wrapped specimens subjected to wet/dry cycling exhibited a higher reduction in strength than those subjected to freeze/thaw cycling. Glass fiber wrapped specimens subjected to wet/dry exposure exhibited about 20% reduction in strength, whereas specimens subjected to freeze/thaw exposure suffered less than 10% reduction in strength. The strength values were presented using Weibull statistics. The rule of mixtures model was used to predict the tensile strength. Fractography was employed to identify the failure initiating flaw and failure mode for the fractured tensile specimens.
WATER INVASION, FREEZING AND THAWING IN CEMENTITIOUS MATERIALS. M. Ausloos, E. Salmon, and N. Vandewalle, S.U.P.R.A.S., Institut de Physique B5, Université de Liège, Liège, BELGIUM.
A model of fluid invasion, freezing and thawing in a porous cementious medium has been elaborated and investigated through numerical simulation. This model has been studied within the invasion percolation ideas. The fluid freezing process is considered as slowly destroying the internal structure of the materials. The evolution of the pore structure after several invasion-frost-thaw events (cycles) has been investigated. The results are qualitatively consistent with experimental findings on composite cements. The cluster size decreases with a power law as a function of invasion-frost-thaw iterations. The fractal dimension of percolating invasion clusters varies with the number of cycles. The avalanches characterizing self-organized systems will be presented. In fact, the successive invasion percolation clusters are found to be self-avoiding with aging.
MECHANICAL STRENGTH ENHANCEMENT OF LOWERED HYDRAULICITY CEMENTITIOUS INORGANIC SOLID WASTES BY USING OF ANHYDRITE AND POZZOLANIC MATERIALS. Seong-Su Hong, Gye-Gyu Lim, Hoseo University, Dept of Chemical Engineering, Chungnam, KOREA; Byoung-Ky Lee, Do-Su Kim, Jae-Seong Rho, Dept of Fine Chemicals Engineering and Chemistry, Chungnam National University, Chungnam, KOREA.
The mechanical strength enhancement of lowered hydraulicity inorganic solid wastes(HISWs) from 5 different manufacturing processes of building materials was investigated for recycling. The source of waste materials used for recycling are cement-gypsum composite board, cement fiber reinforced board, calcium silicate board, corrugated slate, and sludge from wastewater treatment plant. To improve the mechanical strength, powder admixture of anhydrite as an ettringite forming agent and slag/fly ash as pozzolanic materials was added on the basis of weight ratio to cement. The powder admixture had a composition of 80% anhydrite and 20% slag/fly ash. The specimens were prepared by nonpress method and press molding method and cured with steam at 80C. On the contrary of compressive strength and other properties, the flexural strength of HISWs added specimens did not meet the target standards for special use regardless of source processes, addition ratio and preparation methods without powder admixture. The strengths of specimens were decreased with the increasing of addition ratio of HISWs. The long term mechanical strengths of pressed specimens under 50 kgf/cm2 pressure with the addition of 10 wt% powder admixture of anhydrite and slag/fly ash to cement were enhanced due to the stimulated pozzolanic reaction by slag/fly ash and the ettringite formation by anhydrite. The increased intensity of ettringite and CSH peaks was detected in X-ray diffraction patterns and confirmed by SEM and EDS analysis. The flexural strength was markedly increased more than 30% independently of the addition ratio of HISWs and met the specifications. The absorption ratio was also decreased with the addition of powder admixture because the ettringite was formed in microcapillary pores.
SLUMP LOSS CONTROL OF CEMENT PASTE BY ADDING OF POLYCARBOXYLIC TYPE SLUMP-RELEASING DISPERSANT. Gye-Gyu Lim, Seong-Su Hong, Hoseo University, Dept of Chemical Engineering, Chungnam, KOREA; Byoung-Ky Lee, Do-Su Kim, Jae-Seong Rho, Dept of Fine Chemicals Engineering and Chemistry, Chungnam National University, Chungnam, KOREA.
The polycarboxylic type slump-releasing dispersant which is the copolymer of maleic anhydride and acrylic acid(MA-co-AA), was used to compensate the slump loss of cement mixed with naphthalene sulfonate formaldehyde condensate(NSF) dispersant with the hydration time. The average molecular weight of MA-co-AA used in this study was 800. The different ratios of MA-co-AA to NSF which were 0, 10, 20, 30, and 40 wt% were added to the target cement paste in order to evaluate dispersive stability, zeta potential, slump loss, and rheological behavior with the elapsed time. All these results are compared with one another. The mixing of MA-co-AA with NSF resulted in the increase of adsorption amount of dispersant per unit weight of cement. Whereas the differences of the zeta potentials of cement particles were not observed for the different ratio of MA-co-AA to NSF. Especially, NSF containing 20 wt% of MA-co-AA showed an excellent control effect on slump loss of cement paste. In the case of rheological properties, NSF containing 20 wt% of MA-co-AA showed the retaining effect with relative increment of apparent viscosity. The optimum dosages of NSF containing 20 wt% of MA-co-AA for the control of slump loss were 1.5 wt% and 1.0 wt% to cement weight under the condition of 35% of the ratio of water to cement (W/C) and 50%, respectively. Observered was also the optimum dosage of MA-co-AA mixed NSF depends upon the W/C conditions to obtain the effective slump loss control of cement paste. From the results of this research, the slump loss of cement paste could be controlled effectively by the addition of 1.0-1.5 wt% of MA-co-AA mixed NSF.
FABRICATION AND CHARACTERIZATION OF ABSORBENT POLYMER-CEMENT COMPOSITE. Chong-Yoon Rha, Chang-Eun Kim, Dept. of Ceramic Engineering, Yonsei Univ., Ki-il Kim, Dept. of Information, KINITI,Seoul, KOREA.
The cement-absorbent polymer composites were fabricated by semi-powder mixing cements with absorbent polymer absorbed theoretical water content. The effects of absorbent polymer on mechanical/chemical properties of composites were observed. The hydration procedure/ microstructure of composites were studied. The mechanisms of interaction between cement and polymer in the composites was also discussed. Since the cement-absorbent polymer composites were fabricated by homogeneous semi-dry mixing and low water/cement ratio condition, it had less than ten percentage total porosity. Especially, the composite contained relative low volume percentage of pores size with more than 1ß‚, hence the flexural strength of composites improved more than that of neat cement pastes. The average flexural strength was up to 180kgf/cm2 in the case of hydrated composites added with 1wt% absorbent polymer during 28 days. Since the absorbent polymer filled interparticle capillary pores and Calcium-silicate-hydrate in thin plate form dominated, inner microstructure of composite was more dense and capillary pore structure changed intermittently. Accordingly the permeability and the moisture resistance of composite improved. In case of adding absorbent polymer to cements from 0.5wt% to 2.0wt%, retardation of cement hydration has not been observed. The effects of absorbent polymer on the cement-polymer composite contributed not only to physical but also chemical properties of the cement-polymer composite. It was considered in this study that leached multi-valence ions from cement grains during hydration accelerated the extraction of water from absorbent polymer network and played two important roles of polymer-cement interaction.
STUDY ON THE PROPERTIES OF HIGH EARLY STRENGTH DEVELOPING GROUT MATERIALS. Min-Chul Jung and Bang-Yun Han, Research Center of Hanil Cement Co., Ltd., Taejon, KOREA.
Grout materials made with ordinary portland cement have many disadvantage properties, such as drying shringkage, delayed hydration, low compressive strength development etc. Calcium sulphoaluminate mineral (C4A3S) shows many desirable properties which can compensate the undesirable properties of grout materials, such as shrinkage compensate and high early strength development etc. In this study grout materials were made using calcium sulpho- aluminate mineral, ordinary portland cement and anhydrite. The cacium sulphoaluminate modified grout materials were characterized microstructure, flowability and mechanical properties. In addtion, effects of organic materials on the hydration of modified grout materials were studied. The modified grout materials presented high flowability and high strength development at an early hydration time, compared with those of controlled.
STABILITY OF MAGNESIUM POTASSIUM PHOSPHATE CERAMICS*. K.C. Goretta, D. Singh, T.L. Smith, M.M. Cuber, and A.S. Wagh, Energy Technology Division, Argonne National Laboratory, Argonne, IL.
Chemically bonded ceramic composites were prepared from MgO, H2KPO4, and Class F fly ash. Microstructures were examined by X-ray diffraction and scanning electron microscopy, and crushing strength was measured. The stability of these materials was tested by (a) exposing composite specimens to deionized H20 for up to 100 days and (b) heating specimens to l5O-lOOOOC in air. Exposure to H20 decreased the concentration of retained MgO in the microstructure. Strength initially decreased with time in H20, but increased after exposure to H20 for 10 days. Heat treatment decomposed the matrix MgKPO46H20 phase. Substantial strength was, however, retained after heating to 35OC. Because of sintering, strength increased after heating at 1000C. Microstructural changes with heating were complex and will be discussed.
SESSION MM4/JJ3: JOINT SESSION:
NONDESTRUCTIVE CHARACTERIZATION OF CEMENT
Chair: John S. Popovics
Tuesday Morning, December 2, 1997
Independence West (S)
8:30 AM *MM4.1/JJ3.1
DURABLE CONCRETE STRUCTTURES, A PROVEN REALITY OR STILL A DREAM? Carsten Henriksen, IN SITU S.A., LUXEMBOURG; and Claus G. Petersen, German Instruments A/S, Copenhagen, DENMARK.
Durability of reinforced concrete structures today is a hot topic in the concrete industry. The new trend is to specify a service life or 100 years, or more, by means of ``High Performance Concrete'' based on specialized theoretical service life calculations. Quite naturally, such calculations are founded on laboratory methods that reflect the desired, ideal ``lab-crete'' condition. The actual concrete produced on-site, the ``real-crete'', is however, receiving less attention - if any. The paradox is further emphasized by the fact that most durability problems relate to inadequacies created during the construction phase. Today, reliable and well proven in-situ test methods for essential durability aspects of the structure itself are available on the market. However, in general have not been used with a great deal of hesitation, meaning that it is still uncertain if a structure made of high performance concrete - when handed over to the client - in fact is fulfilling the stipulated service life requirements. In essence, the modern concrete world is facing a situation where no serious means of proving the actual durability of the structure is applied. On the other hand, the best intentions are exercised in design, in the choice of materials, in motivation of the workmanship or checking it, and in conducting careful quality assurance programs. Are the well-known mistakes made 25 years ago in relation to durability going to be repeated in the years to come, just in a much bigger scale? The paper presents in-situ methods related to essential durability properties of the structure itself. The methods are for use in the planning stage, during construction and after the construction has been completed. Furthermore, the paper speculates over the reasons for general lack of acceptance of the methods in the concrete industry and suggest means of improving the acceptance/use of the methods.
9:00 AM MM4.2/JJ3.2
INTEGRATED FIBER OPTIC SENSORS FOR NONDESTRUCTIVE CHARACTERIZATION OF CONCRETE STRUCTURES. Farhad Ansari, Smart Sensors & NDT Laboratory, Department of Civil & Environmental Engineering, New Jersey Institute of Technology, Newark, NJ.
In-service performance of structures depends on consistent monitoring of condition for early scheduling of repair and retrofit operations. Early detection of large displacements and cracks m concrete elements will result in increased safety and considerable savings in rehabilitation costs. Optical fiber sensors are emerging as superior nondestructive means for evaluating the condition of concrete structures In contrast to Ousting nondestructive evaluation techniques, optical fibers are able to detect minute variations in structural conditions through remote measurements. It is possible to monitor the initiation and progress of various mechanical or environmentally induced perturbations in concrete elements by way of fully integrated optical fiber sensors. This article is intended for a brief introduction into the theories, principles, and applications of fiber optic sensors as they pertain to civil engineering applications. Most of the civil engineering related research in this field have been focused in applications to concrete. This is due to the geometry adaptability of optical fibers and ease by which they can be embedded within concrete elements. However, due to the fact that the transduction mechanism in optical fibers is invariant of the materials employed, the principles introduced here also correspond to other structural materials. The only application related differences among various materials pertain to sensitivity and choice of optical fiber sensor type.
9:15 AM MM4.3/JJ3.3
A MULTIPLEXED OPTICAL FIBER SENSOR SYSTEM FOR DISTRIBUTED MEASUREMENT OF STRUCTURAL STRAINS. Farhad Ansari, and Zhongyu Chen, Smart Sensors & NDT Laboratory, Department of Civil & Environmental Engineering, New Jersey Institute of Technology, Newark, NJ.
Structurally integrated optical fiber sensors form the basis for smart structure technology. Over the past decade a variety of sensor configurations have been developed for measurement of strains and deformations in structures. Strains and deformations alter the refractive index and the geometry of the optical fiber material. These changes perturb the intensity, phase, and polarization of the light-wave propagating along the probing fiber. The optical perturbations are detected for the determination of strain. The research presented here describes the development of a new optical fiber sensor system for measurement of structural strains based on white light interferometry. An optical switch provides for multiplexing of strain signals from various locations in the structure. Redundant Bragg grating type fiber optic sensors as well as strain gauges were employed for comparison and verification of strain signals as measured by the new system. The system provides capability for distributed sensing of strains in large structures.
9:30 AM MM4.4/JJ3.4
FAILURE LIFETIME PREDICTION OF CRACKED CONCRETE STRUCTURES. Fabrizio Barpi, Silvio Valente, Dept. of Structural Engineering, Politecnico di Torino, ITALY; Francesco Chille', ENEL-CRIS, Milano, ITALY; Lorenzo Imperato, ISMES, Bergamo, ITALY.
When subjected to high tensile stresses, brittle and disordered materials (concrete, rock, ceramics, fiber reinforced composites, etc.) undergo strain-softening, which is localised in a narrow band (process zone), outside which the material behaves linearly. According to cohesive crack model (Barenblatt, Dugdale, Hillerborg), the process zone can be represented as an extended portion of the real crack, called fictitious crack, where the material, albeit damaged, can still transfer stresses. This model can explain the size-effect on many structural responses in both Mode I  and Mixed-mode [2, 3]. Using the finite element method in Mixed-mode problems, a remeshing technique is applied at each crack growth step. Under high level sustained load, creep outside the process zone can be neglected compared to creep in the process zone. In this paper the creep law has been determined experimentally, through a serie of direct tensile tests . The same creep law has been used to simulate 30 three point bending tests (Mode I) and 3 laboratory tests on notched gravity dam models (Mixed-mode, 1:40 scale ). Numerical results were found to be in good agreement with experimental results. The load vs. C.M.O.D. (Crack Mouth Opening Displacement) curves obtained during static tests can be assumed as a valid envelope criterion for creep fracture in Mode I problems (direct tensile tests and three point bending tests). In the Mixed-mode problems analysed creep fracture occurred before the static envelope was reached.
9:45 AM MM4.5/JJ3.5
NON-DESTRUCTIVE EVALUATION OF THE INTERFACE IN REINFORCED CONCRETE USING PHASE MEASUREMENT INTERFEROMETRY. Masoud Ghandehari, Northwestern Univ, Dept of Civil Engineering, Evanston, IL; Sridhar Krishnaswamy, Northwestern Univ, Dept of Mechanical Engineering, Evanston, IL; Surendra Shah, Northwestern Univ, Dept of Civil Engineering, Evanston, IL.
Studying the behavior of steel and concrete as a composite is of fundamental importance to the understanding of the cracking of reinforced concrete structures. In this article, a technique leading toward the development of a constitutive model for the interaction of steel and concrete is described. Experiments are based on pull-out specimens, where the shear stress and the two displacement components at the interface are measured. Phase Measurement Interferometry is used for accurate surface displacement measurement, and crack growth detection. The normal stress is then deduced using the measured crack length and crack opening displacements, along with a fracture mechanics based numerical simulation.
10:30 AM *MM4.6/JJ3.6
CONTINUOUS AIRPORT PAVEMENT DEFLECTION MEASUREMENTS USING A ROLLING DYNAMIC DEFLECTOMETER (RDD). Kenneth H. Stokoe, II, James A. Bay, Michael McNerney, and B. Frank McCullough, Department of Civil Engineering, University of Texas at Austin, Austin, TX.
Nondestructive testing of airport pavement plays an important role in the management of the runway infrastructure. A new technique for continuous profiling of pavements, called the Rolling Dynamic Deflectometer (RDD) has been developed. The RDD is a large truck on which a servo-hydraulic vibrator is mounted. The vibrator is used to apply large vertical dynamic loads to the pavement. The resulting dynamic displacements are measured with rolling sensors. A description of the RDD and procedures used to analyze RDD data are discussed in this paper. The results of continuous RDD profiling of taxiways and runways at the Dallas-Forth Worth Airport are presented. These results show that continuous stiffness profiles of displacement per given load of the pavements can be used to characterize: 1. the pavement stiffness and its longitudinal variation; 2. the location of transverse cracks and joints; 3. the efficiency of transverse cracks and joints; 4. the efficiency of longitudinal joints; and 5. the lateral variation in average mid-span stiffness. Three significant benefits of continuous RDD profiles which are clearly shown are: 1. softer versus stiffer areas are clearly delineated, 2. the variation in joint efficiency is readily identified, and 3. variations with time are readily identified by repeat measurements over time.
11:00 AM MM4.7/JJ3.7
THE LEACHING OF THE REACTIVE POWDER CONCRETE: THE RESULTS ON THE TRANSFER PROPERTIES. Veronique Matte, Bouygues, Direction Scientifique, Challenger, St-Quentin-en-Yvelines, FRANCE; Micheline Moranville, Laboratoire de Mecanique et de Technologie, Cachan, FRANCE.
The Reactive Powder Concrete is a new cementitious material which exhibits a very low porosity and a high compressive strength. In order to study its viability concerning the storage of the nuclear wastes, the RPC is submitted to a water leaching test. The pH is buffered to 7 and the water is often renewed to maintain it deionised. The concentration of the ions released by the the material is measured and expressed as a function of time. The modifications of the transfer properties after leaching are also studied (porosity and diffusion). Concerning the diffusion aspect, two cases are studied:
- The diffusion of an external ion without interaction with the cement paste (tritium);
- The diffusion of the ions coming from the cement paste.
This permits the understanding of the chemical equilibriums that occur during the leaching process. Thus, it could be possible to model the leaching process and predict the RPC's changes due to the leaching for 300 years or more. On the other hand, the modification of the pore distribution due to the leaching process is studied by MIP (Mercury Intrusion Porosimetry), but also by using more powerful techniques like proton NMR, BET (sorption-desorption of water vapour), SAXS (Small Angle X-Ray Scattering) and SANS (Small Amgle Neutron Scattering). In this way, the investigation of the pore structure under 100 angstroms is possible.
11:15 AM MM4.8/JJ3.8
FATIGUE DAMAGE MONITORING IN CONCRETE. Kolluru Subramaniam, John S. Popovics, Surendra P. Shah, Center for Advanced Cement Based Materials, Northwestern University, Evanston, IL.
Rigid airport pavement structures suffer damage from multi-axial high magnitude cyclic stresses resulting from passing heavy aircraft. It is of interest to model the response of plain portland cement concrete to such loading conditions; thus, the sensitive detection and characterization of such damage during the loading process is important. Low strain vibrational resonance frequency measurement offers direct information concerning the global, apparent elastic moduli of the material and preliminary results have shown that such measurements are sensitive to the presence of damage in concrete.
The work reported here includes the theoretical foundation and experimental results of a non-destructive technique, based on vibrational resonance measurement, applied to monitor damage imparted to end-mounted hollow concrete cylinders subjected to monotonic and cyclic torsional (bi-axial) loads. An introduction to the concepts of vibration testing and details of the mechanical and vibrational test procedures employed are given first. The most significant vibrational modes, of all of the possible modes set up within the specimen, are identified. The frequency value of these significant modes in the concrete specimen are experimentally obtained throughout a controlled monotonic testing procedure to failure. Distinctions in the frequency values of the various excited resonance modes are noted. Moreover, effects of the two damage types (monotonic and cyclic) on the frequency values of the modes are studied.
1:30 PM *MM5.1
DSP CEMENT PASTES AND MORTARS: CURRENT STATUS. J. Francis Young, Univ. Illinois, Center Cement Compos. Matls., Urbana, IL.
Partially-packed cement pastes and mortars that are castable at low water eminent ratios are now being used in a variety of technical applications. Silica fume is the predominate fine particle used for packing. This paper will review some of the critical processing issues, such as disperse of silica fume; the basic chemistry and microstructure including how it is modified by silica fume content and the combined effect of silica fume and low watercement ratio on material properties of these systems.
2:00 PM MM5.2
CEMENTITIOUS COMPOSITE MANUFACTURED BY EXTRUSION TECHNIQUE. Bin Mu, Zongjin Li, Stanley N.C. Chui, Jun Peng, Hong Kong Uvin. of Sci. & Tech., Dept. of Civ.& Struct. Eng., Kowloon, HONG KONG.
Easier processing and lower cost comparing with continuous fiber-reinforced composite make the short fiber-reinforced and more desirable. Using extrusion technique, the randomly oriented short fibers can also be approximately aligned in the load direction to enhance stress and toughness capacity of composite. This paper presents the achievement of both theoretical and experimental studies for short fiber-reinforced composite manufactured by extrusion. The cementitious composite in the extruder is considered as a nonlinear viscoelastic fluid. By studying the key parameters of such a fluid, a general nonlinear viscoelastic constitutive model is introduced, in which the effects of the normal stresses are taken into account. The flows in the deep flight extruder are assumed as two dimensional steady shear flows. The differential equations, reflecting the flow motion and constitutive relationship, are numerically solved by the finite difference method. The special requirement of extrusion technique for short fiber-reinforced cementitious composite is further considered using a factor for the purpose of predicting the extruder flow volume rate with a deep channel depth. The viscosities and normal stress coefficients of the cementitious composite with various mixing formulas are measured by a Cone-and-Plate rheometer. The relationship of viscosity to shear rate is used to guide the extrusion process. Cylinders with diameter of 50mm and plates with thickness of 6 mm were produced. Compression test, four point bending test and direction tension test were carried out to investigate the influence of various ingredients and mixing ratios on the composite mechanical properties. The theoretical and experimental results are compared.
2:15 PM MM5.3
PROCESSING OF A PHENOL-RESIN CEMENT COMPOSITE. J. A. Walberer, A.J. McHugh, Univ of Illinois, Dept of Chemical Engineering, Urbana, IL.
Results of experiments on the formation of high-strength composites, based on calcium aluminate cements and a phenolic resin system, will be presented. Processing involves formation of an essentially water-free paste by mixing of the components, followed by pressure curing at high temperature to create a hydrophobic, chemically crosslinked polymer matrix. Torque rheometry in a Banbury mixing system is used in combination with scanning calorimetry (DSC) and NMR to quantify the mechano-chemical structuring that takes place during paste formation and subsequent curing of the hardened composite. The evolution of extensional and shear flow rheological properties of the pastes is also monitored as a function of the mixing history. In addition to their intrinsic importance, such data help to quantify the structure-related relaxation processes that take place prior to, and during, the pressure curing step. Measurements of the mixing torque versus time reveal a mechano-chemical interaction between the organic and reactive ceramic phase, characterized by an induction period of flat torque followed by a period of rapid paste stiffening. The behavior of the induction and stiffening periods as a function of mixing rate, temperature, and pH suggests that a specific sequence of chemical events is responsible for paste development. DSC and NMR data on pastes with different mixing histories lead to a consistent interpretation of the mechanochemistry. Dissolution of the cement during the induction period increases the pH of the paste causing the resin to partially polymerize and ionically interact with the cement particles, thereby rapidly increasing paste stiffness through formation of a network structure. Biaxial flexure strengths of hardened samples are on the same order as the so-called macro-defect-free poly(vinyl alcohol) - cement composites and reveal a sensitive interplay between the mixing-induced rheology and the locking-in of a tight network during the curing step. The implications of these results for the processing of reactive, organo-ceramic composites will also be discussed.
2:30 PM MM5.4
EFFECTS OF ALKALI ON THE PROPERTIES OF BELITE RICH CEMENT. C.-K. Park, S.-Y. Hong, B.-K. Kim and B.-J. Oh, Ssangyong Research Center, Taejon, KOREA.
Belite rich cement present high flowability, low heat liberation and high strength development at a long curing time. These properties are attributed to content of belite and calcium aluminate minerals. Belite rich cements are generally composed of 20-30% alite, 45-60% belite, 2-4% tricalcium aluminate and 9-12% calcium aluminferrite. This mineral composition causes belite rich cements low reactivity, resulting in developing low strength which attributes poor mechanical properties and durability at an early curing time. In this study effects of alkali on formation and hydration of belite mineral and belite rich cements were studied. Alkali influenced stabilization and activation energy of b-C2S. b-C2S stabilized by alkai was more reactive than those stabilized by other stabilizers: much polymerization at an early hydration time. The specimens containing high alkali produces flake type C-S-H gel, while low alkali produced needle type C-S-H gel. For belite rich clinker the alkali was detected abundantly in matrix phase and acted as an activator of hydration, resulting in developing high strength and other mechanical properties at an early curing time.
2:45 PM MM5.5
SALT CRYSTALLIZATION IN PORES. George W. Scherer, Princeton University, Princeton, NJ.
It is well known that when a crystal grows within a pore, it can exert a pressure on the pore wall that is related to the supersaturation of the solution. However, there are other important factors influencing the crystallization pressure so that, at a given supersaturation, different crystals exert different forces. For example, when a columnar crystal spans a pore, the stress it can exert is limited by the yield stress of the crystal. Probably more important is the effect of the interfacial energy between the crystal and the wall: if the crystal wets the surface, then it will not exert any repulsive force (so the crystallization pressure is zero). One indication of the interfacial interaction is the critical growth rate (CGR) below which the advancing interface of the crystal is able to repel a suspended particle; at higher rates, the crystal engulfs the particle. We report the CGR of various salts (including NaCl and Na2SO4) in solutions containing particles of various types of stone and cement. A greater CGR indicates the potential for greater crystallization pressure.
3:00 PM MM5.6
MICROWAVE CURING EFFECTS ON THE 28-DAY STRENGTH OF CEMENTITIOUS MATERIALS. Donggy Sohn and D. Lynn Johnson, Dept. of Materials Science and Engineering, Northwestern University, Evanstown, IL.
Microwave energy can be applied on the curing of the cementitious materials because of their water content. Compared with traditional steam curing, the microwave curing technique has several advantages, such as rapid and uniform heating, less tendency to overheat, as well as rapid heat control. However, previous reports of the effect of microwave curing on 28-day compressive strength are inconsistent. One shortcoming of previous studies is uncertainty about the thermal history of the specimen during curing; typically the power, rather than the temperature, was fixed. Isothermal heating, achieved best by feedback temperature control, is required to properly investigate the temperature effects on the properties. Types I and III Portland cement mortars were cured isothermally with feedback temperature control at several temperatures, and 28-day compressive strengths were measured. Pore solution analysis was also investigated to see whether there were any changes in hydration due to microwave curing. Exploring the possibility of the property improvements, appropriate amounts of pozzolanic materials such as blast furnace slag, silica fume and fly ash were substituted for a portion of the Portland cement and tested.
SESSION MM6: NOVEL SYSTEMS AND APPLICATIONS
Chair: Stephen Kwan
Tuesday Afternoon, December 2, 1997
Independence West (S)
3:30 PM *MM6.1
ALKALI-ACTIVATED CEMENTS: OPPORTUNITIES AND CHALLENGES. Della M. Roy, Materials Research Laboratory, Penn State University, University Park, PA.
Based on a history starting in the `40s, there have been many recent developments in alkali-activated cements. The current status reveals major opportunities for such cements based upon a) substantial knowledge of properties and mechanisms; b) good track record of field performance in various applications and; c) future orientation as environmentally-friendly materials in accord with making use of substantial amounts of by-product and waste materials, thereby consuming less energy and generating less waste. For future needs, limitations, unknowns, research imperatives: a) standards: considerable effort is needed to gain more widespread development through the evolution of more performance-based standards. While Portland cement performance equivalence is one target to aim at, in many cases, the properties of alkali-activated cements, especially durability, are superior; b) development of data base: greater confidence will be gained in the manufacture and use of alkali-activated cements as a more extensive data base is available to improve the predictability of performance; c) greater understanding of the reactivity and reaction mechanisms is required; e.g., slag glasses with Al in 4-coordination appear to be more reactive than those glasses having Al in 6-coordination, but the comparative mechanisms of reaction of different alkali systems are not yet fully understood; d) the variability in compositions of many of the alkali-activated cements requires continued search for, and application of, new characterization methods. It is important for long-term durability to more fully characterize the complex solid phases, including determining the combined state of alkali in the solid hydration products, and of the residual soluble species in the pore fluids as a function of time.
4:00 PM MM6.2
DURABILITY OF OIL-WELLS CEMENTS UNDER HARSH TEMPERATURE CONDITIONS. Christine Noik, Alain Rivereau, I.F.P - Institut Francais du Petrole, Rueil-Malmaison, FRANCE.
Oil-wells with depths exceeding 4000 m and bottomhole temperatures above 150C are common throughout the world. For those harsh temperature conditions it is necessary to strictly control cement reactivity and mechanical properties over the life-time of the well i.e 10 to 15 years. Cement formulations were designed for high temperature and high pressure conditions. The main selection criterium was the thickening time at 180C fixed at 4 hours and the slurry density value fixed at 1.9 or 2.3. Performances of Portland cement containing polymer as retarder and dispersant, silica flour and weighting agents were observed during 2-3 year at temperature up to 180C and pressure of 7MPa. Mechanical properties such as compressive strength, water permeability were correlated to structural evolutions of cement systems observed by DRX and MEB. Main conclusions were:
- Polymer has more influence over time on mechanical properties at temperature below 120C
- Presence of silica limited the evolution of the compressive strength even at 180C
- Structural phases such as tobermorite at 120C and xonolite at 180C has been detected by MEB and DRX
- Presence of ferrite or manganese oxide decreased the mechanical properties of cement depending on the granulometry of the weighting agent.
4:15 PM MM6.3
THE EFFECTS OF SULPHONATED PHENOLIC RESINS ON THE PROPERTIES OF CONCRETE. Sheng-Da Chen, Chih-Horng Hwang, Kung-Chung Hsu, National Taiwan Normal Univ, Dept of Chemistry, Taipei, TAIWAN.
A water soluble solphonated resin (SP) was synthesized from phenol, formaldehyde and sodium bisulfite through a four-step reaction. The synthesized SP could reduce the water content, improve the workability and compressive strength of concrete. The best results were obtained for concrete containing 2 wt% SP, which are comparable with commercial superplasticizers. Thus, SP has the potential to be used as a superplasticizer.
4:30 PM MM6.4
DEVELOPMENT OF AN ADMIXTURE FOR SELF-LEVELLING CONCRETE. Sebastien Rols, Jean Ambroise, and Jean Pera, U.R.G.C. Materiaux, Institut national des Sciences Appliquees de Lyon, Villeurbanne, FRANCE.
In the past decades many efforts have been undertaken to develop highly-workable concrete which consolidates under its own weight without any vibration specially in Japan. The admixtures used in such concrete are mainly composed of high water reducing superplasticizers, fine limestone dust and viscosity agents to maintain not only high flowability but high segregation resistance of the concrete. The water to cement ratio is generally lower than 0.55. New admixtures are proposed in the present study. They consist in mixtures of a superplasticizer and one type of the following viscosity agents: starch precipitated silica, waste from the starch industry. The composition of the self-levelling concrete is as follows. The total amount of fine materials (cement + fly ash or cement + ground limestone) is 400 kg/m3, while the cement content (normal portland cement CEM I 52.5) is 260 kg/m3. The water to cement ratio was in the range of 0.65 to 0.80. The mechanical performances of the hardened concretes are better than those of a usual French building concrete. The 28 day-compressive strengths were in the range of 28 to 43 MPa. The water permeability was in the range of 2.8 x 10-11 to 6.5 x 1012 m/s.
4:45 PM MM6.5
HYDRAULIC CONCRETE AS A DEEP-DRAWING TOOL OF SHEET-STEEL. Arnaud Schwartzentruber, Jean-Pierre Bournazel, Laboratoire de Mecanique et Technologie, Ecole Normale Superieure de Cachan, Cachan, FRANCE; Jean-Noel Gacel, SOLLAC, Centre d'Etudes et de Developpement, Montataire, FRANCE.
Facing up to the increasing competition of aluminium and plastic, the manufacturers of sheet-steel for deep-drawing have to offer to their clients new technical innovations reducing production cost. In the current industrial process, the cost reduction could occur at the stage of tools production. One proposes to produce these tools in concrete. The cost price and difficulties linked to the fabrication are reduced hence decreasing strongly the production cost. The compressive strength of high performance concrete are sufficient for the stress level imposed during a metal forming cycle. Nevertheless the number of cycles is limited by the abrasion of the contact area due to wear. To improve this mechanical characteristic, the first way of research consisted in covering the tool with a gel-coat. The results were satisfactory but the weakness of this technic is located in the interface between concrete and gel-coat. Hence, we steered our researches towards a pure concrete solution. The use of a plastic mould and judicious admixtures allowed us to obtain tools with a marble surface state. Such tools will permit us to suggest in the near future new solutions available from economical and technical points of view.
SESSION MM7: CHARACTERIZATION
Chair: Judy LaRosa-Thompson
Wednesday Morning, December 3, 1997
Independence West (S)
8:30 AM MM7.1
DETERMINATION OF AIR VOID CONTENT AND SIZE DISTRIBUTION IN HARDENED CEMENT PASTES USING THE SECTION ANALYSIS METHOD. Kalliopi K. Aligizaki, Philip D. Cady, Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, PA.
The methods currently used for air void analysis in hardened air entrained concrete are the point count method and the linear traverse method, which have been standardized and are described in detail in ASTM C 457 for use on polished concrete sections. The section analysis method, even though it was mathematically developed much earlier than both the linear traverse and the point count method, has not been used yet in concrete science. The section analysis method requires measuring areas of circles on a concrete section, which is very difficult, if not impossible, to measure with a stereoscopic microscope. However, the section analysis would be very easy to conduct on a concrete section using the currently available technology, i.e., image analyzers. This study used the section analysis method on air entrained pastes to determine the air void parameters and compare the results to the results obtained using the point count method. Five series of air entrained cement pastes were prepared with a water/cement ratio of 0.40, 0.45, 0.50, 0.55 and 0.60, each having an air content of about 1.5%. The point count analysis was carried out using a stereoscopic microscope at a magnification of 50X by counting approximately 500 points on each series. As a first approach, for the section analysis instead of an image analyzer an area of about 100 mm2 from each series was photographed at 80X and reproduced by pasting the photographs next to each other. In addition, the air void size distributions were obtained for each series from the section analysis data using three different calculation procedures. For the size of surface area examined and for the total air void content tested in this study, the results show that the total air void volume calculated by the section analysis method is 1.4% to 34.3% lower than the corresponding values using the point count method. The air void size distributions obtained using the different calculation procedures compared well to each other for all the series. The section analysis method has the major advantage over the point count method that it can provide information on air void size distributions, while the point count method cannot. From a practical viewpoint, the air void size distribution may prove to be a better parameter for characterization the pore structure of air entrained pastes than the parameters used so far, i.e., the specific surface and the spacing factor.
8:45 AM MM7.2
ACTIVE THIN SECTIONS TO STUDY SYNERESIS. Mario de Rooij, Jan Bijen, Dept. of Civil Engineering; G. Frens, Dept. of Chemistry, Delft University of Technology, Delft, THE NETHERLANDS.
Thin sections become more and more important in studying the materials structure of cementitious composites. However, these thin sections are always being made from hardened products. To achieve more information on the hardening process itself, it is all the more tempting to look at an active thin section, i.e. a thin section of a cement paste which is hardening under the microscope. In our research it has been possible to construct these active thin sections. Using ordinary light microscopy it is possible to observe water movement and volume changes on hydrating specimens of about 100 m thickness. We have used these active thin sections to study a phenomenon known in the field of chemistry as syneresis. This process describes the contraction of a gel under the expulsion of a liquid without changing the total volume, This process is thought to play a major role in the formation of the interfacial transition zone. Using the active thin sections it can be shown that water is indeed being pressed out of the cement paste during the first stage of hardening as it should according to the syneresis theory. Since the changes are taking place in a horizontal plane, bleeding is ruled out. Furthermore, experiments show that the more water is being expelled if the cement is finer. This again excludes bleeding, but is in perfect agreement with the laws of colloid chemistry.
9:00 AM MM7.3
X-RAY POWDER DIFFRACTION FROM HYDRATING CEMENT PASTE. Laurie Aldridge, Cliff Ball, Terry Sabine, ANSTO, Menai, AUSTRALIA.
It is difficult to monitor hydration reactions of Portland cement pastes in-situ by Bragg- Brentano x-ray diffraction. This is because; (1) the exposed surface is susceptible to carbonation (2) the sample dehydrates at the exposed surface and (3) the complex pattern of overlapping peaks makes it hard to distinguish the changes. Using synchrotron radiation and image plates in the large Debye camera BIGDIFF on the Australian National Beamline Facility at the Photon Factory in Japan we recorded successive x-ray diffraction patterns of hydrating cements sealed in a glass capillary. Using a Weissenberg screen it was possible to record eighteen patterns at five minute intervals on a single set of plates with a resolution and signal to noise ratio that are superior to that of any conventional x-ray diffractometer. While it is normal practice to completely evacuate the camera before each run we only partially evacuated the camera so that we were able to start the exposure within 6 minutes of mixing. The scattering from the residual air gave a very high background, that obscured the amorphous regions but did not obscure the weak peaks. The hydration process was monitored till 30 hours hydration. While earlier workers have used synchrotron radiation to monitor the hydration of pure phases we believe that this is the first time that it has been used to observe the hydration of cement before, during, and after the induction period of cement hydration. The growth rate of portlandite was measured during the onset of the hydration process for both DSP and ordinary portland cement hydrating pastes. It was also found that during the induction period there was little significant change in the phase content of the two pastes.
9:30 AM *MM7.5
CHARACTERIZATION OF PORTLAND CEMENT CONCRETE MICROSTRUCTURE USING THE SCANNING ACOUSTIC MICROSCOPE. Richard A. Livingston, Exploratory Research Team, McLean, VA; Murli Manghnani, Geophysics Dept., University of Hawaii, Honolulu, HI; and Manika Prasad, Geophysics Lab., Stanford University, Stanford, CA.
The scanning acoustic microscope has been applied to investigate several aspects of Portland cement concrete (PCC) microstructure. This method uses ultrasound to image the local impedance at each point of a material. The impedance image highlights microstructural features that are difficult to observe with other imaging techniques. The topics that have been investigated so far include the influence of aggregate composition on the development of the cement paste/aggregate interface, the nature of interfacial transition zone and ettringite formation. Several types of gels have been observed, which can beiclassified by their characteristic impedance values. Hadley grains have also been identified. Future work includes quantification of impedance values by first arrival times and the identification of PCC phases by ultrasonic impedance spectroscopy.
10:00 AM MM7.6
WATER AND CHLORIDE PERMEABILITY OF MICROCRACKED CONCRETE. Corina-Maria Aldea, Sanjay S. Jaiswal, NSF Center for Advanced Cement Based Materials, Northwestern University, Evanston, IL; Jeff Picka, National Institute of Statistical Sciences, NC; Bruce Ankenman, Dept of Industrial Engineering, Northwestern University, Evanston, IL; Takeru Igusa, NSF Center for Advanced Cement Based Materials, Northwestern University, Evanston, IL; Alan Karr, National Institute of Statistical Sciences, NC; Surendra P. Shah, NSF Center for Advanced Cement Based Materials, Northwestern University, Evanston, IL.
The present research focuses on the relationship between crack characteristics and concrete permeability. A pilot permeability study introducing feedback controlled splitting tests to generate width-controlled cracks in concrete specimens was reported earlier. The present study is an ongoing, large scale extension of the previous work, which is novel in its experimental design and in the parameters it considers. A partial factorial design was chosen that made use of combinations of factor levels that would give the most information about the relationship between measured crack characteristics to permeability, while minimizing the number of experiments. The factors chosen for the design were the material type (paste, mortar, normal strength concrete, and high strength concrete), the thickness of the sample slice cut from a cast cylinder (25 mm and 50 mm), the location of that slice within the cylinder, and the average width of the induced cracks. The feedback controlled splitting test was used to introduce predetermined crack widths ranging from 50 to 350 microns. After unloading, the crack widths were reduced by approximately 50 to 65%, resulting in widths from 13 to 172 microns. Control specimens with no cracks were also tested. The chloride permeability of each slice was estimated by means of the rapid chloride permeability test (RCPT), while water permeability was evaluated by a modified version of a water permeability test developed at the University of Illinois at Urbana Champaign. Preliminary results indicate that the water permeability is significantly more sensitive than conductivity with respect to the crack width used in this study. A model is currently being developed that incorporates characteristics of the crack such as its dimensions and surface roughness, and the properties of the cement, the aggregates and the interfacial zone phases.
10:45 AM MM7.7
RELATIONSHIP BETWEEN MICROSTRUCTURE, MESOSTRUCTURE AND TRANSPORT PROPERTIES IN CEMENT-BASED MATERIALS. Sanjay S. Jaiswal, Takeru Igusa, Surendra P. Shah, NSF Center For Advanced Cement-Based Materials, Northwestern University, Evanston, IL; Trish Styer, Alan Karr, National Institute Of Statistical Sciences, Research Triangle Park, NC.
Permeability of concrete is influenced by characteristics at microscopic (interfacial transition zone, porosity) and mesoscopic (volume fraction of aggregate, aggregate spacing, grading, tortuosity of ion path) levels. The effect of volume fraction of aggregates and grading on chloride permeability was investigated in a study conducted with collaboration of researchers in cement and concrete and statistical sciences. Spherical alumina aggregates of two diamaters (6 mm and 12 mm) were used in a cement paste matrix of water/cement ratio = 0.3. The chloride permeability was measured using Rapid Chloride Permeability Test, ASTM C1202-93. Initial results indicate that a simple definition of tortuosity, ratio of path length of ions and thickness of the slice, and interfacial transition zone (ITZ) around each aggregate can be used to interpret chloride permeability results. Volume fraction lowers the permeability of the material by increasing the tortuosity of the flow path of the ions. At large volume fractions of aggregates, the permeability tends to reach a lower bound. Preliminary models using conductivity indicate that increasing volume fractions of aggregates leads to competing effects of percolation of interfacial transition zones (ITZs), which increases permeability, and reduced cement matrix phase, which decreases permeability. There are also interrelated effects of increased tortuosity, proportion of large to small aggregates, and the redistribution of ionic charges at ITZs. The long-term goal of this project is to develop a comprehensive model for concrete permeability which can be used to develop optimal mix designs.
11:00 AM MM7.8
1H NMR AND DSC/TGA STUDY ON THE THERMAL DEHYDRATION OF TOBERMORITE AND JENNITE. Ping Yu, ACBM Center and Dept of Materials Science and Engineering, Univ of Illinois at Urbana-Champaign, IL; R. James Kirkpatrick, ACBM Center and Dept of Geology, Univ of Illinois at Urbana-Champaign, IL.
Tobermorite and jennite are important model compounds for calcium silicate hydrate (C-S-H) phase of Portland cement. Understanding their behavior during thermal dehydration is important to understanding both the structures and properties of the individual phases and the mechanical and thermal properties of cement paste at elevated temperatures. We present here 1H MAS NMR, DSC and TGA, and XRD data for heated 1.1 nm tobermorite and jennite. Jennite changes to metajennite at 100C by losing part of its interlayer molecular water and becomes amorphous at 350C, losing all of its molecular water. At 860C it undergoes a structural phase transition. 1.1 nm tobermorite loses most of its molecular water by 200C yet maintains its basic layer structure. It loses the remainder of its molecular water and undergoes a phase transition at 450C. It also undergoes an additional phase transition at 850C. The results indicate that tobermorite has greater thermal stability than jennite. Cement pastes containing more tobermorite-like structural elements may be preferable for higher temperature applications. 1H MAS NMR resolves signal from water melecules and Ca-OH linkages, is an effective probe of dehydration, and provides structural information complementary to traditional DSC/TGA data.
11:15 AM MM7.9
TENSILE STRENGTH TESTING OF CEMENTITIOUS MATERIALS UNDER TRIAXIAL LOADING. Shuji Tsubota1, Tahar El-Korchi2, 1Ph.D. Candidate, Worcester Polytechnic Institute, Worcester, MA; 2Associate Professor, Worcester Polytechnic Institute, Worcester, MA.
A tensile failure criterion for cementitious materials under tension-compression loading is developed. This paper describes the experimental and analytical details supporting the tensile failure criterion. Cylindrical mortar specimens were subjected to triaxial stresses using hydraulic pressure. The test applies a tensile stress in the axial direction and compressive stress in the lateral direction (=). A series of six tests were conducted where the applied principal stress ratio (/) varied between 0.21 and 11.5. The results show that an increase in compressive lateral stress decreases the maximum tensile strength. The finite-element method was conducted on the analyses of stress concentration factor (Kt=/). The stress concentration is remarkably increased when the principal-stress ratio is decreased below 1.0. The effect of the lateral pressure was clearly defined by the stress concentration factor. The failure line agrees well with the analytical results. The experimental results are also presented using Weibull statistics. As a comparison, the tensile strength is presented with respect to split tensile, uniaxial compressive strength, and specimen size effect.
11:30 AM MM7.10
EFFECT OF ADMIXTURES ON THE THERMAL AND THERMOMECHANICAL BEHAVIOR OF CEMENT PASTE. Xuli Fu and D.D.L. Chung, Composite Materials Research Laboratory, State University of New York at Buffalo, Buffalo, NY.
The thermal behavior (i.e., thermal conductivity, specific heat and thermal expansion) and thermomechanical behavior (i.e., mechanical behavior upon heating and creep) of cement pastes containing various additives (polymers, silica fume and short carbon fibers were studied). Both latex (20-30% by weight of cement) and methylcellulose (0.4% by weight of cement) were effective for decreasing the thermal conductivity of cement paste, due to the insulating nature of these polymers. The addition of short carbon fibers failed to increase the thermal conductivity of cement paste, due to the increase in air void content. The specific heat was increased by addition of latex, methylcellulose or carbon fibers. The flexural storage modulus decreased gradually with increasing temperature from 30 to 150C for cement pastes, such that the effect was reversible, in contrast to the irreversibility of the weight loss upon heating. Among the admixtures used (latex, methylcellulose and silica fume), silica fume gave the highest flexural storage modulus at all temperatures (30-150C), but also the greatest fractional decrease in modulus upon heating. Methylcellulose (0.4% by weight of cement) gave higher modulus than latex (20-30% by weight of cement). The modulus increased with increasing latex/cement ratio. Plain cement paste (without any admixture) gave the lowest modulus.
11:45 AM MM7.11
THE ELECTRICAL PROPERTIES OF CEMENT-BASED COMPOSITES. J. D. Shane, S. J. Ford, T. O. Mason, H. M. Jennings, Northwestern University, Department of Materials Science and Engineering, Evanston, IL.
Cement paste by itself is a complex electrocomposite system consisting of conductive components (pore fluid), less conductive components (C-S-H gel) and insulating phases (e.g., parent cement grains, CH, etc.). When combined with additional phases, such as aggregate particles or fibers, the electrical response of cement-based composites can be quite complicated and difficult to deconvolute into the contributions of the various components. This paper reports work on electrical characterization of model systems involving ordinary portland cement paste in single combination with particulate or fiber additions. Both insulating and conductive additions were employed. The behavior of insulating particulate (mortar) and fiber-added systems can be explained using existing composite mixing models, taking into account the role of a thin, more conductive, interfacial transition zone (ITZ). The behavior of conductive dispersed-phase composites is more complicated. For example, the incorporation of chopped steel fibers to OPC pastes leads to the formation of an additional arc in the impedance spectra. The roles of percolation and spreading resistance must be considered to successfully model such behavior. Ramifications concerning issues of durability (for mortars) and in-place sensing (for fiber-added concretes) will also be considered.