Civil and Environmental Engineering

A statistical analysis was made using the results of experimental factorial design about the volume of permeable voids (VPV) of recycled aggregate concrete samples using the proceedings of ASTM C 642-97. The recycled aggregates were made from crushed and sieved concrete, mortar and red ceramic. The proposed model shows that the VPV increased for all recycled concrete samples and the recycled red ceramic coarse aggregate is the most influential and the recycled mortar fine aggregate is the lesser one.

This paper reports the results of an experimental investigation into the effects of incorporating varying amounts of expanded polystyrene beads on the engineering properties of high-strength concrete. It was observed that a density reduction of 8.3% caused compressive strength, tensile strength and modulus of elasticity to reduce by 48%, 39% and 15%, respectively. Drying shrinkage was marginally increased and the concrete showed considerable ductility.

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/m 3, 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.

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.

By incorporating lightweight expanded polystyrene aggregate particles in a conventional highstrength concrete mixture, its density could be adjusted to any desired level. The adjusted density concrete can be expected to have reduced strength and stiffness the permeability of concrete would not be affected since the non-water absorbing polystyrene aggregate particles are dispersed randomly in a low permeable cement paste matrix. This paper reports the results of an investigation into the effect of binder material on the compressive strength and drying shrinkage of adjusted density (2150kg/m 3 ) high-performance concrete. Five locally available binder material types were used, namely Types GP, SR and GB cements, and a combination of GP cement and fly ash. The results showed that for the adjusted density concrete, the binder type significantly affected the shrinkage and shrinkage-weight loss relationship, although it had marginal effect on the compressive strength.

Coarse and fine aggregates generated from crushed concrete products for new concrete can be generally accepted only when the properties of recycled aggregate concrete, in addition to the relationships between different properties of such a concrete, are well understood. The results o fan experimental investigation into the relationship of compressive strength to ultrasonic pulse velocity and to rebound number is presented in this paper. It has been observed that for the water-cured concrete the strength-pulse velocity relationship is influenced by the use of the recycled aggregate. For the same value of the pulse velocity, the strength of recycled aggregate concrete is higher than that for the natural aggregate concrete. On the other hand, the strengthrebound number relationship is not affected by the aggregate type used. The combined method of pulse velocity and rebound number for strength estimation is also evaluated.

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 superptasticised 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.

Ferrocement containing steel wire-mesh reinforcement in cement mortar and polystyrene aggregate concrete are combined to
construct a two-layer composite. This paper reports the results of an experimental investigation into the behaviour of this
laminate under pure bending. The parameters studied include the amount of wire-mesh reinforcement in the ferrocement skin,
quality of mortar used in the ferrocement and the quality of the polystyrene aggregate concrete. Using transformed section and
ultimate section principles and conventional reinforced concrete theory, the laminates were analysed and the predicted strength
and deformations were compared with the experimental data.

Waste concrete produced from demolition of concrete structures is an alternative source for the production of concrete
aggregates and acceptance of recycled concrete aggregates for the production of new concrete depends on the quality of them.
This paper discusses results of a series of investigations into the properties of recycled concrete aggregates and the effects of using them on the properties of concrete. Concrete aggregates differ from the natural aggregates due to the presence of a considerable proportion of mortar attached to the natural aggregates and consequently affecting the properties and performance of concrete. The results st..ow that for recycled aggregate concrete, compressive and tensile strengths and modulus are reduced, whereas drying shrinkge and creep are increased. The effect of using concrete fine aggregate on the modulus and shrinkage is less than those produced by the use of concrete coarse aggregate. The strength of recycled aggregate concrete can be recovered by making suitable mix adjustments or by the addition of fly ash or silica fume. Modulus of elasticity, drying shrinkage and creep cannot be fully recovered, by the above methods although improvements were observed.

Self-compacting concrete having enhanced ability to flow is known to have increased segregation and bleeding potential. Any attempt to increase the stability of fresh concrete (cohesiveness) requires using increase amount of fine materials in the mixes. This paper reports an investigation into the development of self-compacting concrete with reduced segregation potential. The self-compacted concrete mix having satisfied the criterion recognized by the differential height method is modified in many ways to increase the fine particle content by replacing partially the fine and coarse aggregates by low-calcium fly ash. The systematic experimental approach showed that partial replacement of coarse and fine aggregate could produce self-compacting concrete with low segregation potential as assessed by the V-Funnel test. The paper reports the results of bleeding test and strength development with age. The results showed that fly ash could be used successfully in producing selfcompacting high-strength concrete with reduced segregation potential.

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.