International Concrete Abstracts Portal

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.

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.

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.

An experimental investigation was performed to determine the hydraulic pressure variation of cementitious based materials (cement paste, limestone paste,concrete, Self compacting concrete (SCC), etc.) during the plastic phase. A method based on measurements of both total lateral pressure and hydraulic pressure, using a noveldevice, has been investigated. Just after mixing, a simultaneous drop of both thehydraulic and the total lateral pressures was recorded, followed by a cancellation of totallateral pressure and a negative value of hydraulic pressure. Compared to other standard methods (Vicat, calorimetry, ultrasonic pulse-echo, etc …), the device was able to givesimple and direct information about the mechanical state of the material, in situ. Thekinetic variation of the hydraulic pressure occurring during the plastic phase of cement pastes using two portland cement fractions and a limestone filler was investigated. Torelate the hydraulic pressure measurements with workability, a study on the evolution of the rheology of the cement paste was conducted. The experiments on standard concretes,which had the same free water content as an equivalent cement paste, show a similar hydraulic pressure variation as long as the pressure is positive. This is not the case for SCC where the observed hydraulic pressure variation is slower and the time of zero pressure is delayed compared to the equivalent cement paste. The presence of limestoneand the HRWRA is the main reason for this retardation effect. In addition, as soon as the pressure becomes negative, due to the presence of aggregates, a delaying effect on the pressure variation was observed. In the end, field test show that the hydraulic pressure device could be used to monitor the field schedule of successive pouring, setting and demolding.

Self-Compacting Concrete (SCC) was developed in the later 1980’s and has attracted a wide interest in the world due to its unique properties. This study investigatesthe workability and earthquake resistance of SCC. Several chemical admixtures are added to the concrete to adjust its workability. The workability of fresh concrete is tested using different methods including slump cone, inversion slump cone, L-box and Orimet apparatus. Then the best SCC mixture ratio is selected for microstructural and earthquakeresistance investigations. The earthquake resistance of SCC is investigated on concrete frame. Two frames with the same size are designed and but one cast with SCC and theother one with ordinary concrete. The two frames are tested under low-cyclic loadingusing MTS loading system. ANSYS software is used to simulate and analyze the statictest. The test results give indication how the materials characteristics and constructability of SCC affect earthquake resistance behavior of the frame.