Abrasion resistance and compressive strength of unprocessed rice husk ash concrete

This paper investigates the effects of adding natural rice husk ash collected from uncontrolled burning and without previous grinding (NRHA) as cement replacement in concrete. To obtain an adequate particle size, NRHA was mixed with coarse aggregate for a convenient period of time before adding the other components. Compressive strength, water absorption, porosity, and abrasion resistance expressed as weight loss were examined. Test results show that decreasing the particle size through mixing with coarse aggregate improved the compressive strength, reduced the permeability, and increased the abrasion resistance of concrete. By mixing NRHA with aggregate for 8 min, abrasion resistance improved by 10.35 and 23.62% over the control concrete at 28 and 91 days, respectively. Incorporating NRHA in concrete by grinding with coarse aggregate during the mixing process could be suitable for making normal-strength concrete and for applications where abrasion resistance is an important parameter. In addition, using NRHA as a partial replacement cement contributes to the reduction of CO2 emissions due to the production of cement

Prediction model for hardened state properties of silica fume and fly ash based seawater concrete incorporating silicomanganese slag

Growing concrete consumption has gradually depleted conventional resources. This research incorporates silicomanganese (SiMn) slag, marine sand and seawater as alternative concreting materials. The use of SiMn slag to replace limestone as coarse aggregate enhances sustainability, though reducing strength and durability of concrete. This research aims to enhance the SiMn slag concrete by incorporating silica fume (SF) and fly ash (FA). The interaction of SF and FA on strength, durability and workability of concrete is investigated by statistically evaluating the experimental result. In this regard, the polynomial function prediction model is developed using the Response Surface Method (RSM) for the optimization of SF and FA contents. Analysis of variance (ANOVA) using p-value at significance level of 0.05 showed that the models were statistically significant and had marginal residual errors. All models had high fitness with R2 value ranging from 0.853 to 0.999. Adequate precision of models was above 4, indicating that the models had a low prediction error and were fit for optimization. Optimization indicated that a combination of 11.5% SF and 16.3% FA produced concrete that met the optimization criteria. Experimental validation showed that the highest prediction error was 3.4% for compressive strength, 3.2% for tensile strength, 4.9% for sorptivity and 18% for chloride permeability. The optimized concrete exhibited compact microstructure with good bonding between aggregate and cement paste. By using the established linear equation with SiMn slag concrete, the models also predicted the compressive strength of limestone concrete containing SF and FA with an error of between 0.9% and 5.4%

Reproducible mini-slump test procedure for measuring the yield stress of cementitious pastes

The mini-slump test is a fast, inexpensive and widely adopted method for evaluating the workability of fresh cementitious pastes. However, this method lacks a standardised procedure for its experimental implementation, which is crucial to guarantee reproducibility and reliability of the test results. This study investigates and proposes a guideline procedure for mini-slump testing, focusing on the influence of key experimental (mixing and testing) parameters on the statistical performance of the results. The importance of preparation of always testing at the same time after mixing, testing each batch once rather than conducting multiple tests on a single batch of material, is highlighted. A set of alkali-activated fly ash-slag pastes, spanning from 1 to 75 Pa yield stresses, were used to validate the test method, by comparison of calculated yield stresses with the results obtained using a conventional vane viscometer. The proposed experimental procedure for mini-slump testing produces highly reproducible results, and the yield stress calculated from mini-slump values correlate very well with those measured by viscometer, in the case of fresh paste of pure shear flow. Mini-slump testing is a reliable method that can be utilised for the assessment of workability of cements

Effects of silica fume fineness on mechanical properties of steel fiber reinforced lightweight concretes subjected to ambient and elevated temperatures exposure

This paper presents the effects of silica fume (SF) fineness and fiber aspect ratios of steel fiber on fresh and harden characteristics of high-strength lightweight concrete containing oil palm shell as coarse aggregates. The effect of elevated temperatures on the residual compressive strength of above concretes is also evaluated in this study. Three different SF fineness of 18400, 21000, and 28000m 2 /kg and 2 different aspect ratios of steel fiber of 40 and 80 are considered. Results show that the increase in SF fineness and steel fiber aspect ratio marginally affect the air-dry density of steel fiber reinforced lightweight high-strength concretes, however, the workability is reduced by about 9% to 14% due to increase in SF fineness. The compressive strength of steel fiber reinforced lightweight concretes at all age increases with increase in SF fineness and an improvement of about 37% is observed at 56days by increasing the SF fineness from 18400 to 28000m 2 /kg. Strong correlations are also observed between the strength improvement factor and the SF fineness. Water absorption of above concretes is also reduced by 3% to 14% due to increase of SF fineness from 18400 to 21000 and 28000m 2 /kg. The increase of SF fineness also significantly reduces the residual compressive strength loss at 300°C and 450°C. This loss of residual compressive strength is lower in lightweight concretes containing 16mm long steel fiber than 8 mm long steel fiber. The existing Eurocode model overestimates the residual compressive strength of steel fiber reinforced lightweight concretes containing no SF, however, this discrepancy is significantly reduced with increase in SF fineness