Purpose This paper aims to inspect the effect of indirect elevated temperature on the mechanical performance of nano silica concrete (NSC). The effect on both compressive and bond strengths is studied. Pre- and post-exposure to elevated temperature ranges of 200 to 600°C is examined. A range covered by three percentages of 1.5, 3 and 4.5 per cent nano silica (NS) in concrete mixes is tested. Design/methodology/approach Pre-exposure mechanical tests (normal conditions – room temperature), using 3 per cent NS in the concrete mix, led to the highest increase in both compressive and bond strengths (43 per cent and 38.5 per cent, respectively), compared to the control mix without NS (based on 28-day results). It is worth noticing that adding NS to the concrete mixes does not have a significant effect on improving early-age strength. Besides, permeability tests are performed on NSC with different NS ratios. NS improved the concrete permeability for all tested percentages of NS. The maximum reduction is accompanied by the maximum percentage used (4.5 per cent NS in the NSC mix), reducing permeability to half the value of the concrete mix without NS. As for post-exposure to elevated-temperature mechanical tests, NSC with 1.5 per cent NS exhibited the lowest loss in strength owing to indirect heat exposure of 600°C; the residual compressive and bond strengths are 73 per cent and 35 per cent, respectively. Findings The dispersion technique of NS has a key role in NSC-distinguished mechanical performance with NSC having lower NS percentages. NS significantly improved bond strength. NS has a remarkable effect on elevated temperature endurance. The bond strength of NSC exposed to elevated temperatures suffered faster deterioration than compressive strength of the exposed NSC. Research limitations/implications A special scale factor needs to be investigated for the NSC. Originality/value Although a lot of effort is placed in evaluating the benefits of using nano materials in structural concrete, this paper presents one of the first outcomes of the thermal effects on concrete mixes with NS as a partial cement replacement.
This paper presents the outcome of the first part of a 3 year project aiming to investigate the effect of elevated temperatures on carbon fibre-reinforced polymer (CFRP) retrofitted structures. Accordingly, different protecting mixes to be used as thermal insulating covers were proposed and evaluated. This experimental program addresses a series of indirect fire tests on reinforced concrete beams retrofitted with CFRP laminates exposed to a temperature of 900 °C (1652 °F) after being protected with ten types of special mortar covers. Materials known for their low coefficient of thermal conductivity were added in certain ratios to form mortars for these protective covers. Tests were carried out in a test furnace designed to produce the standard temperature–time curve specified in ASTM E119–95a. Scale effect was considered by proper adjustment of the exposure time to fire test. Temperature at the CFRP level, just below the protecting covers, was monitored to determine the efficiency of the covers in reducing heat transfer during the fire test. Furthermore, mechanical bending load tests were performed on specimens before and after fire tests to determine reduction in flexure failure load of the specimens due to indirect fire exposure. This reduction was found to vary from 10% to 48% for different tested coatings. In spite of the high damage in the protection covers expressing the lowest performance, reinforced concrete beams were still unaffected and could be restrengthened to return to their original status. Recommendations showing proper thicknesses of application and necessary precautions to be taken when using CFRP in retrofitting reinforced concrete structures to enhance their fire resistance were presented.
This paper presents the outcome of a project funded by Beni-suef University targeting the assessment of the addition of carbon nanotubes (CNTs) to reinforced concrete beams on exposure to elevated temperatures. Tests were carried out in compliance to ASTM E119-95a. Besides, pre and post their exposure to elevated temperature tests, the maximum bending capacity of the beams are evaluated. Standard reinforced concrete beams are cast- with and without Carbon Nanotube (CNT). Tests were performed at two temperature levels 400 °C and 600 °C working around temperature ranges expected to have significant effect on concrete endurance, using both one and two hours exposure. Results proved a positive effect for adding CNT to beams at room temperature. This improvement is slightly affected at 400 °C exposure for 2 hr. On the other hand, exposing CNT beams for 600 °C for two hours reduced the beams capacity by 14% compared to a similar reinforced beam without CNT. It is worth notice that CNT was not burnt but suffered de-bonding. Finally, this investigation implies that CNT can be used as an enhancing element to concrete ductility, with no deterioration in other mechanical characteristics on exposure to drastic thermal conditions.
This paper presents a continuation of the evaluation of utilizing Nano Carbon Tubes (CNTs) in reinforced concrete (CNT-CRETE). The compressive, tensile and bond strengths of the samples with and without CNTs were investigated. Scanning Electron Microscope (SME) was utilized to study the microstructure of the prepared samples. In addition, the corrosion resistance of CNT-CRETE, was measured and compared to traditional concrete. Four mixes were prepared, with 0.01%, 0.02%, and 0.03%, CNTs by weight of cement, along with a control mix without CNTs. The results of the experimental work showed that adding CNTs led to an increase in the compressive, tensile and bond strengths of specimens compared to those of the control specimen. SEM examination for control and CNTs specimens showed that CNTs specimen were well structured compared with the control specimen and this affirms that CNTs act as bridges across micro cracks, which explains the improvement in mechanical properties. The diameter of steel bars played a significant role in failure mechanism for pull-out testing and corrosion resistance. In general, adding CNTs to the concrete mix increased the rate of corrosion for steel bars within the low risk limits. Benefits from using CNTs were limited to moderate. Mineral/chemical admixtures or fibers provide better improvements in the mechanical properties of concrete without the problems associated with dispersing CNTs and the health hazard of handling a Nano material.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.