Abstract
The mechanical characteristics of steel fiber-reinforced lightweight concrete (SFLWC) under high temperatures are studied in this paper. Different concrete matrices, including all-lightweight concrete (ALWC) and semi-lightweight concrete (SLWC), and different steel fibers with hooked ends and crimped shapes are considered as objects. In addition, normal-weight limestone aggregates concrete (NWC), no-fiber ALWC, and SLWC were tested after high-temperature treatment as a control group. The temperature effects on the splitting tensile strength, ultrasonic pulse velocity, compressive stress–strain curve, elastic module, peak strain, and axial compressive strength of the SFLWC were investigated. The results showed that, with increasing exposure temperature, both the axial compressive strength and the elastic modulus decreased, while the axial peak strain has a certain increase, and hence the stress–strain curves were gradually flattened. The toughness of all the concretes increased first and then reduced with increasing temperature, while the specific toughness of all the concretes increased with the increase in temperature. Compared with NWC and SLWC, ALWC had a better capacity to resist high temperatures, especially temperatures > 400 °C. Adding steel fibers can improve the capacity of energy absorption, specific toughness, and residual splitting tensile strength of lightweight concrete (LWC) before and after it is exposed to high temperatures. Based on a regression analysis, a segmented constitutive equation for LWC and SFLWC under uniaxial compression was derived from fitting the experimental findings, and the fitting curve agrees well with the test results.
Highlights
Lightweight concretes (LWC) enjoys the advantages of low density, good sonic and thermal insulation performance, and perfect fire resistance, and have been extensively used as structural and non-structural building materials [1,2]
LWCs can be classified into two types: all-lightweight concretes (ALWCs) and semi-lightweight concretes (SLWCs)
For SLWCs, merely coarse lightweight aggregates (LWAs, these can be characterized by porosity, weakness, and brittleness) are employed, while in ALWCs, fine and coarse LWAs are both applied to reduce the self-weight of the LWC structure
Summary
Lightweight concretes (LWC) enjoys the advantages of low density, good sonic and thermal insulation performance, and perfect fire resistance, and have been extensively used as structural and non-structural building materials [1,2]. Balendran et al [11] studied the influence of steel fiber with a volume content of 1% on the compressive strength of NWC and highstrength LWC, and the test results showed that steel fiber has little influence on the concrete compressive strength. [19] studied the self-compacting concrete with different types of steel fibers, and the result showed that the improvement of the concrete flexural behavior (toughness and flexural strength) by hooked end steel fiber (HF) was better than that of straight steel fiber. Based on the test data, the residual mechanical properties of plain LWC (including ALWC and SLWC) and SFLWC at different temperature levels were expressed as functions of temperature These series of prediction equations will promote the usage of steel fiber and LWC in fire-resistant applications in the construction industry
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