PROPERTIES OF METAKAOLIN CONCRETE – A REVIEW

The use of cement supplementary materials in structural concrete is widely accepted by the construction industry for technical, economical and environmental reasons. Metakaolin (MK), produced by calcining kaolinite at high temperature is suitable for concrete production due to its pozzolanic property. This paper reviews the some of the research published on effects of using MK on engineering properties of structural concrete as a cement replacement material. The review shows that the use of relatively finer MK to partially replace cement reduces the consistency of concrete and enhanced the strengths, deformational and durability properties of concrete. MK is most effective in enhancing compressive strength (particularly at early ages) compared to other strengths and modulus of elasticity was least improved. Drying shrinkage and creep of MK concretes are lower than those for the control concrete. The high pozzolanic reactivity of MK with calcium hydroxide contributes to both porosity reduction and pore-structure refinement in the pastes and concrete. As the consequence, the durability of concrete is improved through increased resistance to chloride penetration and controlled expansion, due to alkali-silica reaction and sodium sulphate attack

Quality Assurance of Shotcrete on a Railway Line Project

Specification for shotcrete specifies control over slump, time lag between batching and placing, compressive strength, shotcrete thickness, density and permeability. The wet-mix shotcrete is required to have quality control over the workability for easy pneumatic placement, minimum rebound and good compaction. This paper reports the quality assurance experience gained from a project involving 2700 cubic metre of shotcrete, during the construction of 35 km long Southern Sydney Freight Line project, lasted over 3 years. The field experience showed that quality assurance specification for shotcrete mix must be followed to ensure the quality of placed shotcrete

Acids attack on silica fume high-strength concrete

This paper reports the results of a study on the corrosion of high strength concrete with silica fume subjected to 15% concentration of sulphuric acid, hydrochloric acid and lactic acid. Silica fume were used to replace 8% and 15% of the cement, by weight. The results showed that partial replacement of cement with silica fume had no effect on lactic acid resistance, improved the hydrochloric acid resistance and worsened the sulphuric acid attack. Sulphuric acid attack resulted in concrete disintegration at an almost constant rate, the hydrochloric attack rate was reduced with time, whereas the lactic acid attack resulted leaching of corrosion products, at a slower rate under stagnant condition

Deformational Behaviour Of FRP Confined Concrete Under Sustained Compression

Confining concrete is an effective method to enhance the strength and ductility of reinforced concrete columns. Fibre reinforced polymer (FRP) composites are emerging as a suitable confining material to replace conventional materials such as steel and fibre-reinforced cement composites. Past research on the behaviour of FRP confined concrete in compression is considerable however limited research has been reported on the behaviour of confined concrete under sustained compressive loading. This paper reports the preliminary results of an experimental investigation on the deforinational behaviour of carbon FRP (CFRP) confined concrete columns under sustained compressive stress levels corresponding to 40% and 60% of the unconfined concrete compressive strength for up to 50 days. The results show that the creep of confined concrete columns is marginally influenced under moderate sustained stress/strength ratios

High-strength self-compacting concrete for sustainable construction

Concrete for sustainable infrastructure construction of civil engineering structures is required to use environmentally friendly concrete-making materials and to minimize both energy and manpower needs in concrete placing.With the intension of improving both environmental and economical sustainability, this study on self-compacting concrete with ground granulated blast furnace slag and recycled concrete aggregate was conducted. This paper reports the results of an experimental investigation into the production and properties of high-strength self-compacting concrete mixes with a combination of Portland cement and ultra-fine slag (up to 50% of cement replacement) and with either natural or recycled concrete coarse aggregate. The strengths development and chloride migration coefficient was evaluated. The use of ultra-fine slag was found to improve the stability of self-compacting concrete independent of the type of coarse aggregate.The use of recycled concrete decreased the strengths and modulus of elasticity and increased the chloride permeability for the high strength self-compacting concrete

Flexural strength of steel fibre reinforced concrete beams

International Journal of Cement Composites and Lightweight Concrete64273-27

Recycling concrete as fine aggregate in concrete

International Journal of Cement Composites and Lightweight Concrete94235-24

Effect of supplementary cementitious materials on the properties of pervious concrete with fixed porosity

Pervious concrete is significantly different to that of conventional concrete as it has the ability to allow water to percolate through it large sized pores. This unique ability presents many environmental benefits such as minimising storm water run-off, recharging groundwater and reducing the heat absorption in the pavement. This paper reports the results of an experimental investigation into the use of supplementary cementitious materials on the properties of pervious concrete (compressive strength, stiffness and water permeability) having the porosity of about 20%. The investigation considered four mixes with the following combinations of cement and supplementary cementitious materials, by weight proportion: (a) 100% cement; (b) 75% cement and 25% fly ash; (c) 92.6% cement and 7.4% silica fume; and (d) 84.2% cement, 8.2% fly ash and 7.6% silica fume. The results showed that the cement replacements with supplementary cementitious materials had improved the compressive strength, reduced modulus of elasticity and decreased the water permeability of pervious concrete with fixed porosity