Disintegration of many concrete pavements (D-cracking, popouts, etc.) exposed to freezing and thawing is often connected with poor physical quality of aggregates used in the concrete. Inability to differentiate between good and poor quality aggregates is due to the lack of appropriate laboratory techniques for aggregate evaluation. A growing shortage of easily available sources of good quality aggregates highlights the need for aggregate classification. A new rapid laboratory test, called RAO-Method, as well as a new pore size distribution index based on the mercury intrusion porosimetry (MIP) analysis, has been proposed to meet engineers' expectations in the field of aggregate classification. An analysis of some research data of the RAO and MIP tests is presented in this paper to illustrate practical usefulness of the techniques. Results of long-term observations of concrete blocks subjected to outdoor conditions and the results of the new laboratory tests of the aggregates previously used in the blocks were compared. The new tests seem to provide means for more successful evaluation of coarse aggregates for purposes of diagnostics, design, and prediction of service life of concrete.

Presents a review of recent research focusing on the durability of concrete and mortar containing rice husk ash (RHA). The purpose of the investigation was to determine the effects of RHA in cement products exposed to hostile environments. Included are the results of laboratory research on hydrochloric acid attack, sulfate attack, alkali-silica reaction, and frost action on mortar or concrete mixtures containing RHA. The results showed that mortar or concrete containing RHA showed a substantial reduction in mass loss on exposure to a hydrochloric acid solution and considerable reduction in alkali-silica and sulfate expansions. Also, the frost resistance of non-air- entrained concrete containing RHA was found to be considerably higher than similar concrete mixtures containing silica fume.

A superworkable concrete, which has excellent deformability and resistance to segregation and can be placed in heavily reinforced formwork without vibrators, was developed and employed in the construction of a 70-story building. The height of the building is 296 m, and the height of the superworkable concrete in the tubular columns is about 40 m. Some of the columns have two diaphragms with opening ratio of seven percent at each joint of column and beams. Before actual construction, the placing of the concrete into three model columns was conducted. From the tests, it was confirmed that the superworkable concrete had excellent filling ability and left no voids under the diaphragms. A 6-m high removable column was set on top of the 40-m high column of the building to check the quality of filled concrete. The superworkable concrete was placed successfully into 66 columns of the tallest building in Japan.

Pier B in the port of Halifax, NS, Canada, was built in 1930-32 using 18,000 tons of calcium aluminate cement (CAC, Ciment Fondu), sea-dredged sand and aggregates and mixing water pumped from an inland freshwater lake. The climatic conditions at Halifax are extremely severe; it is estimated that exposed concrete is subjected to about 100 freezing and thawing cycles per year. Pier B is over sixty years old and in regular service as a container terminal for ocean-going ships. The main structure is permanently submerged in sea water. A protective layer of facing concrete made of both CAC and normal portland cement, cast over the outside faces in the tidal zone, has needed periodic repair. The CAC concrete displays excellent durability with cylinder compressive strengths of 29 to 49 MPa, modulus of elasticity of about 30 GPa, and a Poisson's ratio typical of normal weight concrete. Records indicate that the CAC concrete was cast with a water-cement ratio of 0.5 to 0.6 and a cement content of about 330 kg/m 3. Volume porosity is of the order of 10 percent. The investigation reported here of cores taken from Pier B in 1993 provides a broad characterization and guide for more detailed examinations in a collaborative program, the results of which will be reported as they become available. A particular focus of interest will be the speculative existence of zones of enhanced impermeability on the exposed faces of the concrete, an effect which has been observed in other old CAC structures.

In recent years, highly flowable concrete which can be placed without any consolidation has been widely studied. A basic study on this type of concrete incorporating limestone powder and a method for reducing shrinkage properties of the concrete are presented in this paper. In the mixture proportioning for the concrete, a high-range water-reducing admixture is used to increase the flowability of concrete. A small amount of viscosity-increasing agent is also added to minimize the segregation. Limestone powder, which is a low reactivity material, is used to reduce the heat of cement hydration and shrinkage of concrete. Although drying shrinkage of the highly flowable concrete incorporating limestone powder was smaller than that of ordinary concrete or other highly flowable concretes, shrinkage of the concrete needs to be further reduced so that it will be a crack-free concrete. To accomplish this, a method for reducing drying shrinkage of concrete by applying a shrinkage-reducing agent and an expansive additive was tested and good results obtained.