Effects of testing variables on the measured compressive strength of high-strength (90 MPa) concrete /

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Prediction of compressive strength of SCC and HPC with high volume fly ash using ANN

An artificial neural network (ANN) is presented to predict a 28-day compressive strength of a normal and high strength self compacting concrete (SCC) and high performance concrete (HPC) with high volume fly ash. The ANN is trained by the data available in literature on normal volume fly ash because data on SCC with high volume fly ash is not available in sufficient quantity. Further, while predicting the strength of HPC the same data meant for SCC has been used to train in order to economise on computational effort. The compressive strengths of SCC and HPC as well as slump flow of SCC estimated by the proposed neural network are validated by experimental results.

Experimental study of dynamic compressive behaviour of concrete material reinforced with spiral steel fibres

It has been well demonstrated that the impact loading resistance capacity of the concrete material can be effectively increased by adding fibres. Recent studies proved that compared to other conventional steel fibres, using steel fibres with spiral shape further increases the post-failure energy absorption and crack stopping capacities of concrete because of the better bonds in the concrete matrix and larger deformation ability. The present study conducts high rate impact tests using split Hopkinson pressure bar (SHPB) to further investigate the dynamic compressive properties of spiral fibre reinforced concrete (SFRC). SFRC specimens with different volume fractions of fibres ranging from zero to 1.5% are prepared and tested. The influences of different volume fractions of fibres on strength, stress-strain relation and energy absorption of SFRC specimens under quasi-static and dynamic loadings are studied. In SHPB compression tests, the strain rate achieved ranges from 50 1/s to 200 1/s. Highspeed camera is used to capture the failure processes and failure modes of SFRC specimens with different fibre volume fractions during the tests for comparison. Dynamic stress-strain curves under different strain rates are derived. The energy absorption capacities of the tested specimens are obtained and compared. Strain rate effects on the compressive strength are also discussed. The corresponding empirical DIF (dynamic increase factor) relations for SFRC are proposed.

Processing and compressive strength of Al-Li-SiCp composites fabricated by a compound billet technique

Al-Li-SiCp composites were fabricated by a simple and cost effective stir casting technique. A compound billet technique has been developed to overcome the problems encountered during hot extrusion of these composites. After successful fabrication hardness measurement and room temperature compressive test were carried out on 8090 Al and its composites reinforced with 8, 12 and 18vol.% SiC particles in as extruded and peak aged conditions. The addition of SiC increases the hardness. 0.2% proof stress and compressive strength of Al-Li-8%SiC and Al-Li-12%SiC composites are higher than the unreinforced alloy. in case of the Al-Li-18%SiC composite, the 0.2% proof stress and compressive strength were higher than the unreinforced alloy but lower than those of Al-Li-8%SiC and Al-Li-12%SiC composites. This is attributed to clustering of particles and poor interfacial bonding.

Nonlinear fracture properties of concrete-concrete interfaces

The fracture properties of different concrete-concrete interfaces are determined using the Bazant's size effect model. The size effect on fracture properties are analyzed using the boundary effect model proposed by Wittmann and his co-workers. The interface properties at micro-level are analyzed through depth sensing micro-indentation and scanning electron microscopy. Geometrically similar beam specimens of different sizes having a transverse interface between two different strengths of concrete are tested under three-point bending in a closed loop servo-controlled machine with crack mouth opening displacement control. The fracture properties such as, fracture energy (G(f)), length of process zone (c(f)), brittleness number (beta), critical mode I stress intensity factor (K-ic), critical crack tip opening displacement CTODc (delta(c)), transitional ligament length to free boundary (a(j)), crack growth resistance curve and micro-hardness are determined. It is seen that the above fracture properties decrease as the difference between the compressive strength of concrete on either side of the interface increases. (C) 2010 Elsevier Ltd. All rights reserved.

Compressive strength of epoxy with bimodal filling of flyash

Compressive strength of epoxy with "free-inforcement" flyash without any prior separation is studied. It is observed that the increase in filler volume fraction beyond 10% brings about a reduction in the compressive strength. Increasing adhesion factor, determined relative to unfilled matrix, implied an alleviation in the interfacial adhesion due to dewetting, especially at the surfaces of larger particles and at higher filler concentrations. Such deductions were verified by examining the surface features of compression tested samples in Scanning Electron Microscope.