International Concrete Abstracts Portal

The stability of highly fluid self-consolidating concrete (SCC)can be achieved by using a viscosity-modifying admixture (VMA).Currently, there are several types of VMAs available in the market place.Three of the most common ones are based on cellulose-ethers, biopolymers and synthetic polymers. The properties of these three typesof VMAs were studied and compared. Specifically, the influence of thesethree types of VMAs on the properties of self-consolidating concrete (SCCwas studied. Particular attention was placed on the influence of eachVMA on the following characteristics of the SCC: 1) dose response of high range water reducer (HRWR), 2) dose response of air entrainingagent (AEA), 3) stability of the mixture, 4) effects on time of setting and 5compressive strength development.

The challenge in producing successful self-consolidating concrete (SCC) is based on consistently achieving high flow and high stability. The foundation of high quality SCC production is the suitability of the underlying materials and a mixture design that is optimized for those materials and the application. Not all applications require relatively high slump flows in the range of 28-30 inches (700-750mm), where control measures need to be especially well managed. Furthermore, even the best mixture designs can have stability limitations. To assure that SCC applications proceed with minimal difficulties, the concrete producer must anticipate variations in materials and production operations through effective quality control procedures. Changes in cement reactivity, aggregate properties (gradation, shape, and water demand), free moisture, and extra sources of moisture that may be present, for instance, in the truck, and the mixing process need to be carefully monitored. This paper will discuss specific examples that demonstrate best practices in mixture design, QA/QC, and production techniques.

An experimental investigation was carried out to evaluate the effect of high-range water reducing admixture (HRWRA), viscosity-enhancing admixture (VEA), andbinder type on key workability characteristics of self-consolidating concrete (SCC),including retention of deformability, passing ability, and stability. Concrete-equivalent mortar (CEM) mixtures were prepared to evaluate the effect of admixture-binder combinations on flow characteristics, including minimum water content (MWC) toinitiate flow and relative water demand (RWD) to increase a given fluidity. Fourpolycarboxylate-based HRWRAs, a polynaphthalene sulfonate-based HRWRA, four types of VEAs, and three blended cements were evaluated. In total, 16 SCC mixtureswith initial slump flow consistency of 660 20 mm and air volume of 6.5 1.5%, and 17CEM mixtures were investigated. Flow characteristics of SCC and CEM mixtures made with a number of admixture-binder combinations indicate that the efficiency of admixture-binder combination depends on water-to-cementitious material ratio (w/cm), type of binder, and type of admixtures. TheCEM approach can be used to evaluate the effect of admixture-binder combination on flow characteristics because the increase in MWC to initiate flow of CEM corresponds tohigher demand in HRWRA in SCC mixtures. Binder type was shown to have marked influence on the retention of slump flow, L-box and V-funnel passing ability, fillingcapacity, and surface settlement characteristics. The binder type also affects HRWRA and air-entraining admixture (AEA) demand. As established from CEMs, B3 quaternary cement with the smallest 50% passing diameter had the highest MWC (lowest packingdensity) needed to initiate flow and the highest RWD (highest robustness to changes in water). SCCs made with such quaternary cement and polycarboxylate-based HRWRA also exhibited the highest HRWRA demand compared those prepared with other blended cements. Both sets of SCCs made with 0.35 w/cm and 0.42 w/cm plus VEA had similar HRWRA demand and static stability when the polycarboxylate-based HRWRA was used.

Chemical admixtures and mineral powders are often used together in self-consolidating concrete (SCC) to achieve required flowability, passing ability and good segregation resistance. In this study, coal fly ash, blast furnace slag, limestone dust and ground glass powder are used as mineral powders. Different amounts of superplasticizer are added to give the same initial flowability. The properties of both fresh and hardened SCCs are measured. All these SCCs exhibit similar flowability changes with time except the SCCs with limestone powder lose their flowability faster than the rest. Although SCCs with fly ash and glass powder show similar flowability with time during initial time period, they have different setting times. Because blast furnace slag is a cementitious material, fly ash and glass powder are pozzolanic materials, and limestone dust is neither a cementitious nor a pozzolanic material, SCCs with slag exhibit the highest and SCCs with limestone dust the lowest strength from one to 28 days. However, the SCCs with limestone dust show the lowest autogenous and drying shrinkage among the four SCCs.

An experimental program which aimed at investigating the behavior of SCC containingClass F fly ash has been carried out. The fresh state properties of the concrete wereassessed using methods of segregation and flow. The rheology of the paste matrix wasalso characterized and compared with a previously developed paste rheology model. Inaddition, compressive strength, chloride permeability, and mold-finish were evaluated. The results indicate that it is possible to develop a SCC containing Class F fly ash that is high performing in its fresh state. Furthermore, the addition of fly ash was shown toreduce superplasticizer dosage, increase workability, and increase overall chloride permeability resistance. In addition, it was determined that the difference of densities between the aggregate and matrix influence the results of a previously developed pasterheology model.