The objective of this research is to study the compressive strength of mortar due to pozzolanic reaction of fly ash with different particle sizes. Fly ash and river sand which were ground to have median particle sizes of 19.4, 13.8, 6.3 pm and 20.6, 11.7, 6.4 µm, were used to replace portland cement type I at the rate of 10, 20, 30, and 40% by weight of cementitious materials to cast mortar. The pozzolanic reaction, without packing effect, of fly ash mortar is obtained from the difference of compressive strength between ground fly ash mortar and ground river sand mortar which have approximately the same particle size (19.4 and 20.6 pm, 13.8 and 11.7 µm, 6.3 and 6.4 µm) and the same replacement. The results showed that the pozzolanic reaction of fly ash mortar in-creases with the increase of fly ash fineness, age of mortar, and percent replacement of fly ash. Ground fly ash with particle sizes between 6.3 to 19.4 µm have slight packing effect on compressive strength of mortar. At early ages, the contribution to compressive strength of fly ash mortar due to pozzolanic reaction is slight, but it significantly in-creases at later ages. With 40% replacement of 6.3 pm particle size of fly ash, the compressive strength of mortar due to pozzolanic reaction at the age of 90-day is more than 50% of the total compressive strength of mortar.

Macro- and micro-cell corrosion of steel bars in pre-cracked prism specimens ex-posed to marine environment for 15 years are summarized here. The size of the specimens was 100xlOOx600 mm. W/C were 0.45 and 0.55. The specimens were made with ordinary portland, slag (Types A, B and C), and fly ash (Type B) cements. A round steel bar of diameter 9 mm was embedded at the center in each specimen. Crack widths were varied from 0.1 to 5.0 mm. Chloride concentrations in the concrete, micro- and macro-cell corrosion, passivity grade, anodic polarization curve, deposits in the crack, and pit depths over the steel bars were investigated. Dense microstructure of concrete made with a large amount of slag (SCB, SCC) causes accumulation of more chloride in the vicinity of the unhealed cracks (>0.5 mm). However, it does not lead to a remarkable amount of corrosion at the cracked region compared to the other cements after 15 years of exposure. Narrower cracks (5-0.5 mm) as well as the debonded areas in the vicinity of the root of the crack over the steel bars heal irrespective of the cement types. It improves the passivity of the steel bar at the cracked region. Relations between pit depth and crack widths; and macro-cell and micro-cell corrosion are proposed.

It is well known that supplementary cementing materials can enhance the durability of concrete structures particularly in the hot and severe environment. In this study, concrete specimens containing different supplementary cementing materials, namely; silica fume, slag, a natural pozzolan (trass), and mixtures of cement and two pozzolans have been investigated. The tests conducted include, compressive strength, permeability, chloride diffusion, corrosion of reinforcing bars, and carbonation depth, all at different ages. The variables were cement types, supplementary cementing materials, water-cement ratio, and cover thicknesses. After standard curing, concrete specimens were transferred to the Gulf region and maintained in submerged, wetting and drying and coastal environments. For exposure to alternate cycles of wetting and drying, known as the most severe condition, the superior performance of silica fume was followed by the concrete mixture containing trass. However, all concrete mixtures containing natural or artificial pozzolans showed better performance compared with the portland cement control concrete mixtures.

The influence of ground granulated blast-furnace (GGBF) slag on autogenous shrinkage in concrete with a water/cementitious material (w/cm) of 0.3 and 91-day strength in excess of 80 MPa was investigated under tropical conditions. Cement re-placement percentages of 30, 50, 65 and 80% by GGBF slag were examined as well as the finenesses of 4200, 6000 and 7900 cm2/g for the 65% replacement percentage. The GGBF slag increased significantly the cumulative autogenous shrinkage for all replacement percentages and fineness levels tested. The increased autogenous strain occurred within the first 14 days when hydration would have been dominated by the portland cement component, well before significant additional hydration or pore refinement would have been possible due to hydration of the GGBF slag component. This suggests that the driving force for autogenous shrinkage in GGBF slag concrete may differ fundamentally from that for portland cement and silica fume concrete. Possible mechanisms for the increased early autogenous shrinkage in GGBF slag concrete are discussed.

The early age strength development of concretes containing fly ash and ground granulated blast furnace slag has been investigated in order to give guidance for their use in fast track construction. Their use in concrete, although economic, has not gained popularity in fast track construction because of the slower strength gain of these concretes at standard curing temperatures. There are however indications that these cement replacements are heavily penalised by the standard curing regimes. The continuous measurement of the in situ temperatures during a UK Concrete Society Core Project has allowed the early age strength development of concretes in full-scale structural elements to be monitored. The effects of a range of environmental conditions and structural element parameters, including cement replacements, on the early age temperature history and hence the strength development of these concretes has been quantified. High early age temperatures are shown to be especially beneficial to ground granulated blast furnace slag concretes.