Journal Dec 2021

Green concrete with high quality recycled concrete aggregate for precast elements: mechanical properties at early ages Zeger Sierens, Brecht Vandevyvere, Xiaoguang Chen, Jiabin Li

With the development of waste management and recycling technology, it is possible to produce high quality recycled concrete aggregate (HiRCA) on an industrial scale through proper selecting the source of waste concrete and an optimized crushing process. The use of HiRCA in concrete has attracted many interests of industry, especially of the precast concrete sector to improve the sustainability of the products. This paper presents an extensive laboratory study on the strength and modulus of elasticity of concrete containing a HiRCA at early ages. The effect of the HiRCA on the development of the concrete compressive strength, tensile splitting strength, and modulus of elasticity with time is extensively examined by use of an industrial precast concrete mixture. The test variables include the HiRCA content (replacement percentage to natural aggregate by volume) and curing condition (water-cured and air-cured). The test results reveal that the incorporation of the HiRCA has a negative effect on the compressive strength development for water-cured concrete specimens; while it has no remarkable influence on the time-dependent compressive strength for air-cured concrete as well as the tensile splitting strength and modulus of elasticity of concrete. A comparison of the test data with predictions of equations in some existing design codes and standards developed for conventional concrete with natural aggregate is also carried out. It is found that those equations generally provide satisfactory descriptions of the effect of time on the strength and modulus of elasticity of concrete with the HiRCA.

Investigations on fresh and hardened state properties of selfcompacting composite cement concrete Nisheeth Agnihotri, Ravi Agarwal, U.S. Vidyarthi

Properties in fresh and hardened state of self-compacting concrete (SCC) decide its performance and long-term durability of structure. The construction projects often find it difficult to mobilize/transport external mineral admixtures due to the project geography and economy. Alternatively, usage of composite cement which is more environment-friendly, may reap benefits to the project. In order to study the behavior of SCC in fresh and hardened state, an experimental program has been charted out with composite cement as pozzolana portland cement (PPC) and total 16 nos. of SCC mixes were taken into the consideration. The trials were conducted to determine fresh properties and tests such as slump flow, J-Ring, L-Box, V-funnel, and U-Box were conducted. To analyze the properties in hardened state, compressive strength, and split tensile strength test were carried out. The study mainly provides a brief summation to site quality control of SCC vis-à-vis gives an insight on rheological properties, mix design process of SCC, its variations with respect to water-powder ratio and paste volume while using the composite cement.

Optimization and modeling of porous concrete made of ceramic waste, silica fume, and fly ash A. Sofi, Abhinav Bhatt, Rajesh Kumar, Saurabh Chauhan

Ceramic products are part of the essential construction materials used in most buildings. Some common manufactured ceramics include wall tiles, floor tiles, sanitary ware, household ceramics, and technical ceramics. They are mostly produced using natural materials that contain high content of clay minerals. However, despite the ornamental benefits of ceramics, its wastes among others cause a lot of nuisance to the environment. This study focuses on using ceramic waste as a partial replacement of coarse aggregate, the percentage used was 10, 20 and 30%. An amorphous ultrafine powder collected as a by product of the silicon and ferrosilicon alloy production is silica fume. Silica fume is a pozzolanic material which can be used in concrete. Hence in this study silica fume was used as replacement of cement in various percentages such as 10, 20, and 30%. Fly ash is by product collected from thermal power station. Due to its pozzolanic properties fly ash is used as a replacement for Portland cement in concrete. Fly ash was replaced with cement by 20, 30, and 40%. Workability of fresh concrete was checked through slump test. The concrete specimens were tested for compressive strength, flexural strength, split tensile, and water absorption. Upon use of various dosages of fly ash, silica fume, and ceramic waste, fly ash of 20%, silica fume of 10% and ceramic waste of 10% found to be optimum dosage based on mechanical properties of test results. The water absorption test showed that the absorption rate increases with an increase in replacement percentage. The sample with 40% fly ash as replacement has higher absorption than a sample with 30% fly ash as replacement. The ceramic waste replacement showed the least absorption rate among all the three replacement under study, with 1.56% being the absorption rate for 30% replacement and 1.43% for 10% replacement of coarse aggregate by ceramic waste. Based on the obtained experimental results analysis of variance (ANOVA) was conducted with the aim of analyzing the influence of fly ash, silica fume and ceramic waste.

Chloride ingression and capillary water absorption of coal bottom ash based concrete Navdeep Singh

The investigation covers the outcomes of chloride ingression and water absorption tests of concrete containing coal bottom ash (CBA) as a substitute for Portland cement (PC) and Fine natural aggregates (FNA) simultaneously. The compressive strength tests were also performed along with aforementioned. The investigation inferred that as the level of the CBA increases, the resistance towards the chloride penetration also increases while the resistance towards the water absorption decreases. Based on the current investigation, both durability aspects were found to increase for combined/joint replacement of PC and FNA for concrete up to the level of 10% and 25%, respectively.

Properties of waste fiber reinforced cement mortar Basil Al-Shathr, Haider Abdulhameed, Mohammed Mahdi

Cement mortar rendering suffers from cracking due to shrinkage. This research aims to find the optimum content of chopped rubber tires that can be added as fibers to cement mortar to improve their properties.

The chopped fibers were added to the mortar mix in two size groups, first passing sieve 4.75 mm and remain on 2.36 mm (size group 1). While the other passing 2.36 mm and remain on a 1.18 mm sieve (size group 2). Both fiber groups were added at 1, 2, and 3% by volume of mortar.

Results indicate that using the larger size of rubber fibers improves the strength of cement mortar reinforced with them more than when using lower size. Also, the optimum content of fibers that can be added to cement mortar is 2% by volume. The compressive strength, direct tensile strength, and flexural strength of mortar using first size group are improved by 7.2, 45.3, and 18.4% respectively, and drying shrinkage decrease by 7.3% with respect to reference mixture without fibers.

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