R. Sri Ravindrarajah

Properties of hardened concrete containing treated expanded polystyrene beads

This paper reports the results of an experimental investigation into the properties of hardened concrete containing chemically treated expanded polystyrene beads. The results showed that the strength, stiffness and chemical resistance of polystyrene aggregate concrete of a constant density were affected by the water to cement ratio. Drying shrinkage after 84 days of drying for polystyrene concretes, having 10 mm coarse aggregate and a nominal density of 1300 kg/m3, were 730 and 655 microstrains. Empirical equations were developed to relate the strength and pulse velocity and to predict the modulus of elasticity from its strength.

RECYCLING CONCRETE AS FINE AGGREGATE IN CONCRETE

Abstract Increasing shortage of natural aggregates for concrete in urban areas leads to a search for aggregates from new sources. This paper examines the use of crushed concrete fines (CCF) produced from ‘waste’ concrete as fine aggregate in concrete. Tests were carried out to study the properties of crushed concrete fines and the properties of concrete incorporating them. The results show that the modulus of elasticity, pulse velocity, and the long-term properties such as drying shrinkage and creep are significantly affected. It has been found that the detrimental effects of using crushed concrete fines in concrete can be mitigated by a partial replacement of crushed concrete fines with pulverised fuel ash (pfa).

Usage of cement kiln dust in concrete

Abstract Cement kiln dust, a waste material in the cement industry, contains partially processed raw materials. This paper reports an investigation into its usage in concrete as a partial replacement for cement. The percentages of cement replacement by weight were 0, 25, 50, 75 and 100 in cement paste and 0, 15, 25, 35 and 45 in both 1:1.5:3 and 1:2:4 concretes. The results showed that the kiln dust is a cementitious material and it causes the following effects when used as cement replacement: 1. 1. retards the setting of cement; 2. 2. increases the water demand for a constant consistency; and 3. 3. decreases the concrete strength. For the same workability concrete, cement can be replaced by up to 15 per cent with cement kiln dust without causing significant strength loss.

Flexural strength of steel fibre reinforced concrete beams

Abstract This paper describes the influence of steel fibre distribution on the ultimate strength of concrete beams. The effect of delayed casting between the plain concrete and fibre concrete layers on the ultimate strength of concrete beams is also investigated. For the same amount of fibres used, strength of (partially) reinforced beams with fibres in the bottom layer only is about 25% more than that for fully reinforced beams. The presence of fibres in the compression zone does not significantly improve the beam strength. A delay in casting between the plain concrete and fibre concrete layers does not significantly change the ultimate strength of partially fibre reinforced concrete beams.

Properties of pervious concrete containing fly ash

Pervious concrete is one of the most effective pavement materials to address a number of important environmental issues, such as recharging groundwater and reducing stormwater runoff. In this paper, the findings of an experimental investigation on properties of pervious concrete are reported and discussed. The amount of general purpose Portland cement has been reduced by introducing fly ash as a cementitious agent in pervious concrete samples. The properties of various pervious concrete samples including density, porosity, compressive strength, water permeability and drying shrinkage have been carefully measured. In addition, the relationships among these properties are explored. According to the results, high porosity samples indicated higher permeability, whereas their compressive strength was reduced. There was no significant difference between properties of pervious concrete samples containing fly ash and those samples comprising only cement as a cementitious agent. Hence, environmentally friendly pervious concrete with fly ash can be produced in lieu of conventional pervious concrete.

Load effects on fracture of concrete

Failure of concrete under any type of loading is associated with the development of visible cracks and very large inelastic deformations. These cracks are the precipitation of internal microcracks under high strains. The concrete system consists of microcracks even before the application of load. These microcracks propagate under different types of loading to form failure planes with a resulting loss in structural strength leading to failure. This paper discusses the formation of microcracks in concrete under short-term and sustained loadings. Concrete specimens were subjected to constant and incremental sustained loading and the deformations observed are related to the intensity of microcracking. The results show that at equal strains, the degree of internal microcracking is considerably reduced if the sustained load is applied incrementally over a period of time rather than applied as a step. It is concluded that the development of combined bond and mortar cracks is essential to cause failure under sustained loading. The longer the time to failure the higher the intensity of internal cracking at failure.

Casting delay om workability and strength of concrete

Abstract Placing of concrete may be delayed from the time of mixing due to many reasons. This investigation showed that although the delay causes considerable loss in workability, there was no detrimental effect on compressive strength for concretes with or without set-retarding admixture or superplasticizer. Incremental addition of superplasticizer was capable of maintaining the concrete slump within a small variation throughout the delay period. The effectiveness of superplasticizer to improve the workability was found to be a function of initial slump and the age of fresh concrete.

Retempering of plain and super plasticised concretes

Abstract This paper evaluates the use of water, superplasticiser and cement slurry as retempering agents for plain and superplasticised concretes. Water, the most economical retempering agent, produces significant loss in strength of concrete particularly for the superplasticised concrete. Cement slurry, although producing restoration of slump with no significant effect on strength, results in less workable concrete mix due to stickiness effect from the high cement content. Superplasticiser, despite its cost and influence of increasing the rate of slump loss, is the best retempering agent with any loss in strength.

EVALUATION OF FOLDING TECHNIQUE FOR FERROCEMENT ROOFING ELEMENTS.

One of the successful applications of ferrocement is in the construction of roofing elements for houses and industrial buildings. Folded plate roofing elements can be made using two techniques, namely conventional moulding and folding. Advantages of the folding technique over the moulding technique are ease of casting and curing, economy, and uniformity of the elements. Tests carried out with model specimens, having trapezoidal type cross-section indicated that the strength and stiffness of the specimens are not affected by the method of construction. Considering the economy of construction, the folding technique provides an attractive alternative in the construction of folded plate roofing elements.

Technical notes: Additional data on the phenomenon of the effect of presustained loading

Abstract Results of an experimental investigation into the effects of presustained compressive and flexural loading on the strength of concrete in compression and flexure respectively are presented. The parameters considered were load duration, load intensity and age of loading. While the presustained flexural load reduces the ultimate strength capacity of concrete in flexure, the presustained compression improves the strength of concrete in compression. The time-dependent processes which contribute to these behaviour are discussed.