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In this study the effect of two different curing-agents has been examined in order to compare them for optimizing the performance of concrete. The first used type is the Pre-soaked lightweight aggregate (leca) with different ratios; 0.0%, 10%, 15% and 20% of volume of sand, and the second type is a chemical agent of polyethylene-glycol (Ch.) with different percentages; 1%, 2% and 3% of weight of cement. In the test programme performed in this study, three cement content; 300, 400 and 500 kg/m 3 , three different water-cement ratios; 0.5, 0.4, and 0.3, and two magnitudes of silica fume as a pozzolanic additive; 0.0% and 15% of cement weight, were used. The physical properties of concrete were evaluated at different ages, up to 28 days. The concrete specimens are subjected to dry-air curing regime (25°c) during the experiment.The results show that the use of self-curing agent (Ch.) in concrete effectively improves the physical properties compared with conventional concrete. On the other hand, up to 15% saturated leca was effective while 20% saturated leca was effective for permeability and mass loss but adversely affects the sorptivity and volumetric water absorption. Self-curing agent Ch. was more effective than self-curing agent leca. In all cases, both 2% Ch. and 15% leca were the optimum values. Higher cement content and/or lower water-cement ratio leads to more effective results of self-curing agents in concrete. Incorporation of silica fume into concrete mixtures enhances all physical properties.

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To modify high-performance concrete (HPC) fireproofing properties, black sand (BS) was partially substituted as fine aggregate at various levels. This study aims at evaluating the BS reliability in improving HPC durability properties for various construction applications based on its unique heavy minerals. To achieve this, five HPC series blends were setup to substitute fine aggregate independently with BS. Substitution percentages ranged from 15 to 100% with consistent supplementary cementing materials (SCMs) proportion for each gathering. Tests were performed to assess compressive strength before and after fire exposure under various temperatures of 250, 500 and 750 °C at different curing age. Generally, blending FA with BS was better than using SF with BS. Utilizing BS in the range of 15 to 60% as fine aggregate with 10% FA improves HPC fire-insulating properties. Besides, Z1 SEM analysis observed homogenously and compacted HPC microstructure at 250 and 500 °C. Doi: 10.28991/cej-2021-03091634 Full Text: PDF

In concrete, cracking is a common phenomenon due to its relatively low tensile strength‎ ‎, which occurs due to external loads and imposed deformations‎‎. The main research objective is to create a kind of self-healing concrete by employing mineral producing bacteria Bacillus pasteurii‎ to locate the rift in the most favourable circumstances for autogenous healing to take place. Self-healing concrete containing bacteria has been generated for this study through the application of bacterial self-healing elements as ‎spores ‎and nutrients with different percentages of bacteria ranging from (10% - 25%) as a replacement of mixing water is added at the time of pouring. The bacteria influence was observed by Scanning Electron Microscope (SEM) and with Energy ‎Dispersive X-ray Spectrometer. The mechanical properties and durability of a thirty-five mixture were ‎examined. The optimal blending content proportion was ‎10SF20BC, which showed an increment in compressive strength and flexural strength compared to the control mixture ‎to ‎reach 79.16%, 50% respectively and 24.38% enhancement in sulfate resistance. The highest percentage of calcium carbonate precipitations was ‎9.49% of a weight of ‎mixtures ‎elements, which, in turn, revealed the highest area repair rate, which was able to fill the ‎crack with widths leads to 0.80 mm.