To investigate the rheological properties of binders for self-compacting high-performance concrete, six mixtures of self-compacting concrete were initially prepared and tested to estimate their self-compacting property. Then, the binders used in self-compacting concrete were tested for rheological properties using a rotary rheometer. Binders with different water-binder ratios and flow values were also examined to evaluate their rheological characteristics. The binders were composed of normal portland cement, fly ash, two types of ground blast-furnace slag, and limestone powder. The flow curves of binders were obtained by the rotary rheometer with shear rate control. Slump flow, O-funnel time, Box, and L-flow tests were used to estimate self-compacting property of concrete. The flow curves of binders for self-compacting concrete have negligible yield stresses and show an approximately linear behavior at higher shear rates beyond certain limits. Test results also indicate that the binders incorporating fly ash are more appropriate than the other types of binders for quality control of self-compacting concrete.

An investigation was carried out to study the effect of steel fibers in improving the performance of concrete under impact loading. Both conventionally reinforced and fiber reinforced concrete slabs were considered. 50mm thick slabs of size 1OOOmm square clamped on all four edges were tested on a span of 900mm. Hooked-end steel fibers having an aspect ratio of 60 with volume fractions of 1% and 2% were studied. The instrumented drop-weight impact setup developed is capable of dropping a 40kg mass from heights of up to 4.5m. The transient impact load on the instrumented striking head, accelerations of the slab, steel strains, and concrete strains, were all recorded using a high-speed data acquisition system. The cracking pattern and the damage due to impact were examined. The study confirmed the superior impact resistance of steel fiber reinforced concrete.

The harsh environmental conditions in the Arabian Gulf region calls for the use of high performance concrete and utilizing the recent developments in concrete technology in terms of materials and practices to produce concrete with high quality. This paper presents results of an investigation to evaluate the effect of curing and the addition of polypropylene fibers on the properties of high strength concrete. In this study, four high strength mixes with compressive strengths in the range of 65 to 80 MPa were made and tested. The first was a plain mix with a cementitious content of 450 kg/m3, the second was a plain mix with polypropyplene fibers, the third was a silica-fume blended mix (10% cement replacement), and the fourth was a silica-fume mix with polypropylene fibers. These specimens were subjected to three curing conditions: moist curing, dry curing and use of curing compound. The specimens were tested for compressive strength, tensile strength, drying shrinkage and plastic shrinkage cracking. The results clearly show the importance of curing on the quality of concrete. The use of silica fume contributes to the increase of concrete strength and reduction of drying shrinkage. The results also show the contribution of polypropylene fibers in reducing plastic shrinkage cracking and the need for early curing to prevent plastic shrinkage cracking in fresh concrete.

An experimental study was designed to accomplish the following: 1) Compare strengths of cylinders prepared by vibration or rodding following current ASTM C 3 1 and C 192 requirements for the number of layers; 2) investigate whether the experience of the operator affects cylinder strength when vibration and rodding are used to consolidate the specimens; and 3) compare the strengths of 100 x 200-mm rodded cylinders prepared by using two or three layers. Two experiments were designed: 1) a half-fraction, factorial design with the following factors: cement content, slump, cylinder size, consolidation method, and operator; and 2) a comparative design to compare the strengths of 100-mm diameter cylinders rodded using two or three layers with the strengths of 150-mm diameter cylinders. The following summarizes the observations from the first experiment: Overall, the 100-mm cylinders (three layers) were 1.5% stronger than the 150-mm cylinders. However, due to a significant interaction effect of size*cement content; there was a 3.4% difference at the high cement content and no statistically significant difference at the low cement content. Overall, the rodded cylinders were 4.2% stronger than the vibrated cylinders. There was a significant interaction effect of method*size; therefore, the rodded 100-mm cylinders were 7.4% stronger than the vibrated 100-mm cylinders, but there was no difference between the 1 50-mm cylinders prepared by the two methods. Also, the rodded 100-m cylinders were 4.6% stronger than the rodded 150-mm cylinders, but the vibrated 150-mm cylinders were 1.6% stronger than the vibrated 100-mm cylinders. The experience of the operator had no effect. There was no significant interaction between slump and method. There was no significant interaction between cement content and method. In the second experiment it was found that the strength differences between 100-mm and 150-mm rodded cylinders were reduced by one-half when two layers, instead of three were, were used to cast the 100-mm cylinders.

High performance concrete can be used as a vault sealing material in nuclear fuel waste chambers deep in the rock mass and can then be subjected to a triaxial-stress state and a maximum temperature in excess of 200 OC. Triaxial compression measurements at high temperature and pressure have been carried out on high performance concrete specimens. The experiments consisted of measuring in cylindrical specimens subjected to several conditions involving four triaxial loading conditions (03 = 0, 10, 20, and 40 MPa), two testing temperatures (T = 20 and 200 “C), two curing periods (28 and 90 days), a saturated moisture condition, two types of concrete mixtures (type H and type K). Testing was carried out to determine the way in which the physical stability, strength, and deformability of HPC subjected to ambient and high temperature conditions. The testing program shows that the triaxial strength increases with the increasing of the confining pressure and cure period at a constant temperature. The effect of confining pressure and cure period become less critical at high temperature and confining pressure. With increasing temperature at a constant confining pressure, the triaxial strength decreases especially at higher confining pressure ( a3 = 40 MPa). When the temperature and confining pressure were raised, the angles of internal friction !D and the Hoek Brown material constant m decrease, but the cohesive strength increase. High performance concrete at room and high temperature conditions shows elastic-brittle and quasi-elastic-brittle properties, respectively.