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In this paper, the possibility of utilising coarse recycled concrete aggregate (CRCA) obtained from a construction and demolition waste (CDW) plant in Delhi to make 60 MPa self-compacted concrete (SCC) was evaluated. The CRCA was used in as-collected condition and was not processed any further. The aggregate packing (bulk) density (APD) method was adopted to prepare the SCC-CRCA mixture in order to obtain an aggregate mixture exhibiting maximum bulk density/least void content (45%). In addition, SCC was made using aggregate mixtures in which the natural coarse aggregate (NCA) was replaced with CRCA at 0%, 20% and 100% of the total coarse aggregate content by weight. The cement, fly ash, silica fume and water were kept constant for all SCC mixtures. The effects of CRCA on the flow behaviour, mechanical strength, shrinkage characteristics and microstructure properties of SCC mixtures were evaluated. The test results indicated that SCC mixtures made with up to 45% CRCA replacement can be used for structural concrete, which is higher than that recommended in Indian (20%) and international specifications (35%) for traditionally vibrated (conventional) concrete. [ABSTRACT FROM AUTHOR]

The current study reports on the long-term structural performance of novel reinforced marine geopolymer concrete beams under accelerated weathering conditions. The study covers the flexural performance of 40 geopolymer concrete beams reinforced with basalt fibre-reinforced polymer (BFRP) bars, including 12 beams under sustained loading when exposed to 3, 6 and 12 months of accelerated marine environment consisting of tidal cycles of seawater at a temperature of 50°C. The experimental results revealed that the novel marine geopolymer concrete reinforced with BFRP bars reported minimal micro- and macro-mechanical degradation compared to geopolymer concrete or ordinary concrete beams under the same exposure environment, with and without sustained loading. The BFRP-reinforced self-compacting geopolymer concrete (SCGC) beams reported 87% residual ultimate load after 12 months of exposure to marine environments, while the sustained loaded BFRP-SCGC beams reported a residual strength of 79%. In addition, microstructural assessment using scanning electron microscopy and energy dispersive X-ray spectroscopy analysis revealed that after 12 months of exposure there was a trace of chloride salts, indicating the chemical ingress over time; however, the impact on structural properties is not distinct. [ABSTRACT FROM AUTHOR]

In this paper, the bond behaviour of reinforced concrete exposed to high temperature at early age has been investigated. The influence of temperature, curing age before exposing to high temperature and repair agent on the ultimate bond stress and bond displacement of reinforced concrete are analysed. The ultimate bond stress of specimens decreases with the increase in temperature, while the ultimate bond displacement increases with the increase in temperature. After being subjected to the same temperatures, the ultimate bond stress of the specimen heated at a curing age of 28 d is found to be lower than that of specimens that were heated at curing ages of 3, 7 and 14 d. However, the ultimate bond displacement of the specimen heated at the age of 28 d is larger than that of specimens heated at the ages of 3, 7 and 14 d. The ultimate bond stress of the specimen using a repair agent is greater than the ultimate bond stress of the specimen without using the repair agent. On the contrary, the ultimate bond displacement of the specimen using a repair agent is found to be less than that of the specimen without using a repair agent. [ABSTRACT FROM AUTHOR]

An experimental investigation is conducted on the influence of the degradation of fibre-reinforced-polymer (FRP) bars on their bond performance with concrete. A basalt fibre-reinforced vinyl ester (BV) bar, basalt fibre-reinforced epoxy (BE) bar, carbon fibre-reinforced epoxy (CE) bar and E-glass-fibre-reinforced vinyl ester (GV) bar are adopted. The bars are pre-exposed to 40°C alkaline solution for 0, 15, 30 and 45 d and then tested under a direct pull-out condition. The test parameters include the resin type, fibre type and conditioned age. The test results indicate that, for the unconditioned bars, the bond strength of CE bars is the largest, next are the GV bars and BE bars, whose strengths are very close to each other, and the BV bars have the least bond strength. For the conditioned FRP bars, the bond strength retention of BE bars with an epoxy matrix are generally greater than those of BV bars with a vinyl ester matrix. The bond strengths of the conditioned CE bars and BE bars with the epoxy matrix both increase, whereas the BV bars and GV bars show a decreasing trend. It is concluded that the order of bond durability is CE > BE > GV > BV for the bars used in this paper combining the test results with a mechanism analysis. [ABSTRACT FROM AUTHOR]

An innovative hybrid fibre system of steel fibres, polyvinyl alcohol (PVA) fibres and inexpensive (approximately US$230/t) calcium carbonate whiskers (CW) was assessed as a way of improving the mechanical behaviour of fibre-reinforced concrete under static and impact loads and reducing production costs. Static mechanical properties and repeated drop-weight impact tests of the designed hybrid-fibre-reinforced cementitious composites (HyFRCCs) are presented in this paper. The reinforcing effect of the new hybrid fibre system was found to be very close to that of conventional HyFRCCs (incorporating only steel and PVA fibres) under both static and impact loads. It is thus suggested that steel and PVA fibres can be partly replaced with CW to reduce production costs in large-scale construction applications. Ultrasonic pulse velocity, dynamic elastic modulus and crack width assessments were carried out to quantify the degree of damage in samples during mechanical testing. The impact energy absorbed by the specimens could be predicted using linear modelling. There is therefore potential for using such tools to evaluate the in situ structural damage under dynamic loads. [ABSTRACT FROM AUTHOR]