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Curing of concrete is impaired by exposure to drying at early ages. Removing water from the surface layers restricts the binder reactions and pore structure development. High porosity in the surface region will allow the ingress of deleterious agents, which can lead to durability problems. Present work reports results obtained by hydrating a flyash blended cement under drying conditions. Comparisons are made with similar results from a portland cement. Small samples of OPC/pfa (70/30) paste with a water binder ratio of 0.59, initially cured under saturated conditions for 7 days, were exposed at 20 C in a CO2-free environment, to various preselected relative humidities. After 28 and 91 days, the extent of reaction and the porosities of the samples were measured by thermogravimetry and methanol adsorption, respectively. Results show the extent of hydration falls when changing from saturated to 70 percent relative humidity (rh) conditions; below this rh, it is virtually constant. From the shape of the TGA curve, it seems that there is little change in the nature of the gel phase. The pozzolanic reaction appeared to cease below 80 percent rh. Total porosity only fell very slightly with increasing relative humidity even after 91 days exposure. Under drying conditions (70 percent rh) the large-diameter porosity was three times greater than large-diameter porosity obtained under saturated conditions. From these tests it is clear that to promote reaction and to effect a decrease in the volume of large pores, the relative humidity must be greater than 95 percent, at least during early-age curing.

A study was conducted to determine whether pulverized fuel ash, granulated blast furnace slag, and natural pozzolana contribute effective alkalies and whether such alkalies lead to alkali-silica reaction (ASR) damage. Mortar bars were prepared in accordance with ASTM C 227 but stored at 20 C, and using three factory-produced cements, three Type F pulverized fuel ashes, three blast furnace slags, and four natural pozzolans at three or four different levels of substitution. The reactive aggregate component was Beltane opal substituted at the pessimum level, as well as zero and three near-pessimum levels. The selection of the materials and their substitution levels were adjudged to represent as wide as possible present-day usage. Deleterious expansion defined as > 0.0 percent within 4 years was taken as the criterion of failure. The results have been applied to demonstrate the deduction of practical guidelines for the use of composite hydraulic binders in situations in which ASR is a consideration. Limiting total alkali contents of composite hydraulic binders as function of the substitution ratio of the three mineral additives are suggested. The analysis of the results demonstrates that if the effective alkalies derived from portland cement are taken as 100 percent, then those derived from pulverized fuel ash and natural pozzolana can be taken as 17 percent and those derived from blast furnace slag as 50 percent of total alkalies. There is also evidence of somem mineral additives, particularly at high substitution levels, not simply acting as dilutents but exhibiting a positive ASR-suppressive effect.

Paper presents the results of the tests conducted on reactive andesite produced to determine if Japanese fly ashes produced in Japan have an effect in controlling the alkali-aggregate reactions in concrete. Fourteen fly ashes produced were subjected to Japan Industrial Standard (JIS) alkali-silica reaction (ASR) mortar bar test (40 x 40 x 160 mm, alkali content in cement 1.2 percent, s/a = 2.25) with (c + f) ranging from 5 to 30 percent. With f/(c + f) at 20 percent or higher, all the mortar test bars incorporating fly ash had little expansion even after 6 months, but with f/(c + f) at 10 percent, different expansions were produced depending on the type used. The analysis of the data indicated that the component Na2Oeq of fly ash would accelerate the expansion while the component SiO2 will restrain the expansion. The controlling ability is also related to the alkali content of the cement: the greater the alkali from the cement and fly ash, the greater the quantity of fly ash required for preventing the expansion. An empirical formula expressing such a relationship has been derived. 123-389

Cements consisting of 60 percent ground granulated blast furnace slag and 40 percent fly ash activated by 7 percent sodium hydroxide have been investigated. Various slags were used, including some laboratory-made synthetic slags. The influence of additives like superplasticizers and defoaming agents has been examined. The most favorable composition with respect to strength development has been subjected to a durability testing program. A negative aspect appeared to be the carbonation resistance, which is low in comparison with portland cement. Carbonation leads to a decrease in strength. Other properties were favorable.

Rice husk ash (RHA) was obtained under different burning conditions from 400 to 1200 C. The changes in the properties of RHA were investigated by XRD, DAT, and microanalytical techniques. When RHA obtained at different burning conditions was added to cement paste or mortar, several properties such as hydration, setting time, porosity, and strength revealed changes.