The strength and toughness durability of carbon fiber reinforced cements (CFRC) in inorganic acidic environments was investigated by subjected prismatic flexural specimens (15 x 15 x 150 mm) to two acidic environments (H2 and HNO4) at the age of 28 days for up to 90 days. The pH of the two acids was maintained at 4.0. Eight CFRC mixes and three volume fractions of pitch-based carbon fibers were investigated. It was concluded that while plain unreinforced cements had considerable retrogression in their mechanical properties, carbon fiber reinforced cements had no appreciable effect on either the strength or the toughness, at least for the duration of exposure investigated.

To determine the characteristics of deterioration of concrete under freezing and thawing, acoustic emissions of mortar were measured and analyzed. Acoustic emissions of the ice formation were examined to establish test conditions. In addition, propagation properties of acoustic emissions, such as wave velocity and amplitude, were examined with an acoustic emission (AE) pulser. The test results for water showed that acoustic emissions due to ice formation took place during both thawing and freezing. The test results with mortar showed that most acoustic emissions occur during the freezing and that the number of acoustic emissions does not increase with the number of freezing and thawing cycles. The test also showed that the propagation of acoustic emissions is effected by air content and curing period. Therefore, the propagation properties must be considered to evaluate the frost damage of mortar with acoustic emission events. Further, wave velocity and amplitude measured with an AE pulser decrease as the number of freezing and thawing cycles increase. It is concluded that the wave velocity and amplitude of AE pulse propagation can be used as indicators to evaluate the degree of frost damage of mortar.

Laboratory tank tests were used to assess the sulfate resistance of a series of portland and blast furnace slag cement concretes. Following different early curing regimes, 100 mm concrete cubes were stored in tanks of sodium and magnesium sulfate solutions for 5 years. The concrete cubes were photographed, and their sulfate attack ratings and compressive strengths measured at 1, 2, and 5 years. The results showed that concretes made with ground granulated or pelletized blast furnace slag and portland cement generally had good sulfate-resisting properties when the slag content was 70 percent and above. The significance of the precuring regime, the tricalcium aluminate (C3A) content of the portland cement, and alumina level of the slag on the sulfate resistance of concrete are discussed. A degree of carbonation of the concrete prior to storage in the sulfate solutions was found extremely beneficial in the prevention of sulfate attack. Sulfate-resisting portland cement (SRPC) of low tricalcium aluminate content and combinations of high tricalcium aluminate ordinary portland cement (OPC) with low alumina slags were shown very resistant after 5 years in high-strength sulfate solutions. The concrete cube results were compared with data previously obtained using the same series of cements in small-scale accelerated methods of test, and a reasonable correspondence was found. Recommendations are made for an acceptance test for determining the sulfate resistance of cements and for maintaining good concrete performance in sulfate conditions. The BRE tank test is a severe test, and its relevance to the ultimate behavior of concretes in the field is discussed.

The durability in seawater of high-strength concretes produced with the addition of silica fume replacing a part of the cement was investigated. The influence of the wet-curing time on the behavior in seawater of high-strength mortars (strength in excess of 60 MPa) in which a part of the cement was replaced by densified silica fume, was determined. The various curing times applied to the specimens, after mold removal, were 48 hr, 7 days, and 28 days at 100 percent relative humidity, followed by storage for 28 days at 20 C and 50 percent relative humidity before the start of tests for resistance to seawater for 1 year. Investigation of the porosity of these mortars shows that, just after curing, the silica fume, as expected, reduces the total porosity of the reference mortar (25 to 45 percent) and substantially alters the pore-size distribution--the shorter the curing time, the more marked this effect. However, as hydration continues at 50 percent RH, the porosity of the reference mortar decreases and the differences in total porosity with respect to the mortars containing silica fume become smaller--the longer the initial curing time and the higher the C3 A content of the cement, the greater this effect. This explains the results of resistance to seawater, where it is found that silica fume contents of less than 10 percent do not lead to any significant improvement in behavior in seawater. This shows that the type of curing and the ambient conditions under which strength increases may limit the beneficial effects of silica fume on durability, when the addition of the silica fume is accompanied by a corresponding reduction of the cement content. It is also found that the best curing method is the specimens in fresh water for the first 7 days, while a curing time of only 48 hr is highly detrimental in terms of the subsequent behavior of the mortars in seawater.

An investigation has been carried out on the effects of cement replacement by fly ash on the carbonation rate of concrete. The research was mainly devoted to portland blast furnace slag cement because this cement has a major market share in the Netherlands. It has been concluded that in the case of portland blast furnace slag cement concrete, replacement up to 25 percent by mass results in a substantially higher carbonation rate, while for a similar portland-cement concrete, the difference between concrete with and without replacement is relatively small. This observation corresponds with the finding that the pH development of the pore water in concrete with portland blast furnace slag cement is too low to initiate a substantial fly ash dissolution. As a consequence, pozzolanic activity will be slight. However, in portland-cement concrete, pozzolanic action can develop more effectively and contribute to strength and densification of the matrix. A useful relation exists between the carbonation depth after 1 or 2 years and compressive strength after 28 days and, even better, after 7 days for each type of cement. This relation might cover all types of cements when the lime content of the binder is involved.