International Concrete Abstracts Portal

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 paper presents studies on local bond and bond strength of splices. The study was conducted in two stages. In the first stage, an analytical equation was developed to calculate the bond strength of splices in normal strength concrete. The mean value of test/calculated bond strength for the proposed equation is 1.007 with a standard deviation of 0.08 1. The second stage of the study comprised the study on local bond and the bond strength of splices in the case of high performance concrete (HPC)/high strength concrete (HSC). The study on local bond involved tests on forty five short length specimens. Using these test results, a relationship for bond strength normalised with respect to the tensile strength of concrete is obtained. The study of bond in splices involved tests on twenty two beams made of HPC/HSC. In each beam, the tensile steel was spliced in the constant moment zone. Using the relationship for local bond in HPC/HSC, the analytical model developed for normal strength concrete is modified. Good correlation between calculated and test strengths of splices in the case of HPC/HSC is found.

In this research, the effectiveness of zeolite, silica fume and fly ash in making high performance concrete with a strength range between 50 and 120 Mpa and a slump around 2OOmm is compared. In the first series of experiments, the results showed that zeolite could decrease bleeding, and increase marginally the viscosity of concrete without significantly compromising the slump. Although zeolite could not increase the strength of concrete as high as silica fume, it performed better than fly ash due to much finer and high content of soluble Si02. At 15% replacement of cement by zeolite, it could result in 14% increase of concrete strength at 28-day compared with the control concrete without any mineral admixture. The test results also showed that although the replacement percentages of cement from 5 up to 15% by zeolite, silica fume and fly ash could all raise the 7 and 28-day strength of concrete, there existed an optimum replacement percentage for the admixtures to effect a decrease in ISA, and in chloride diffusivity of concrete. In the second series of experiments, the test results confirmed that zeolite could perform better than fly ash but was inferior to silica fume in terms of increasing strength and improving permeation characteristics. It was further found that when w/(c+p) was greater than 0.45, the strength of the concretes incorporating zeolite or fly ash (by direct replacement) would decrease. The test results alsoshowed that zeolite could reduce the diffusion of chloride into concretes. The micro-structural study on concrete with zeolite revealed that the soluble SiO, and A1203 could react with Ca(OH), to produce C-S-H which could densify the concrete matrix. Furthermore, zeolite could have the refinement effect on the pore structure of hardened cement paste, decreasing the content of the harmful large pores, hence making concrete more impervious.

A cement of high fineness (Microfine@ Cement) was specified for grouting the dry joints in the Huites Dam by Lombardi Consultants, Zurich, Switzerland. The first half of the paper contains specifications on the Microfine Cements by Onoda Cement in Japan and test data on the Microfine Cements developed at Northwestern University under the direction of Professor Raymond Krizek. The second half includes specification and application of 120 metric tonnes of Microfine Cement into the dry joints of the Huites Dam. The Huite Dam is located over the Fuerte River in the north part of Sinoloa State, Mexico. The dam will regulate the flow of the river, provide 440 megawatts of electricity and irrigation waters for 70000 hectacres. Total reservoir capacity is 4568 million cubic metres. In March of 1995, the dam construction was completed and the reservoir was filled. For structural reasons, it was necessary joints before the concrete reaghed 24 &o inject some opened slightly on reaching 24 C. C, the joints Therefore, it was necessary to reinject Microfine Cement, the product that had been approved for use at this building site.

Foamcrete, also known as foamed or cellular concrete is a lightweight material that can be used for the development of infrastructure to the benefit of disadvantaged communities. The objective of this paper is to discuss the tests conducted on foamcrete using South African materials. The cost of foamcrete can be reduced by replacing large percentages of the cement with ungraded ash. This replacement does not lead to noticeable reductions in compressive strength, but the shrinkage is markedly reduced. Reinforcing bars can be used in foamcrete but although no problems have been encountered with bond, the low shear strength of foamcrete can lead to premature failure. The use of chopped polypropylene fiber improves the shear behavior of small structural elements to the extend that the load-deflection behavior of foamcrete beams are similar to that of comparable normal concrete beams.