Studies were done on the physical, mechanical, and geochemical properties of candidate cementitious materials for sealing a geologic nuclear waste repository in a tuff host rock environment. One sanded cementitious grout contains substantial replacement of cement by low-calcium fly ash and silica fume, yet maintains a water-cementitious solid ratio of 0.32 for a fluid grout. The ash and fume were used to achieve a higher SiO2 and Al2O3 content more compatible with the tuff geochemistry than a plain portland cement. One possible application for such materials is fracture sealing near waste canister emplacement holes. The effects of temperatures from 15 to 300 C on the material properties were investigated. Initial compressive strengths of materials cured at 38 C for 7 to 900 days ranged from 100 to 125 MPa. Other properties investigated include bond strength (to tuff), water permeability, interfacial permeability, Young's modulus, density, porosity, expansive stress, and phase changes. Samples heated to 150 C for extended periods (28 days), either dry or hydrothermally, maintained their strength and well-bonded microstructure, while the results of heating at 300 C were mixed, with some strengths remaining high (95 to 110 MPa) and others diminishing (44 to 51 MPa). The water permeability did not increase much at 150 C but did increase at 300 C.

Quality and performance of site-stored concrete blocks and structural-quality concretes from actual structures, where concretes contained different levels of ground granulated blast furnace slag as cement replacement material, have been assessed in terms of carbonation and gas or water permeability. First, 100 and 150 mm concrete cores were cut from site-stored concrete blocks and tested to assess the coring techniques and methods of measuring properties. These provided data on depths of carbonation and nitrogen, oxygen, and water permeability of ordinary portland cement and blast furnace slag cement concretes. Second, concrete cores were taken from actual structures. The two main factors influencing the depth of carbonation were the level of slag replacement for portland cement and the environmental conditions in which the concretes were situated. Carbonation was greater in the higher slag content cements especially if associated with a sheltered or drying microclimate. However, in general, gas and water permeability decreased with increased portland cement content and as slag replacement levels were reduced from 70 to 50 percent. Based upon these observations, appropriate slag contents are recommended for future use in various types of in situ concrete element.

Since 1971, a contracting firm has produced approximately 1.3 million m3 of high-strength concrete for offshore platforms in the North Sea. The major part of this concrete volume has been produced without condensed silica fume (CSF), fly ash, or any other pozzolanic material. For the company's latest project, moderate dosages of CSF in combination with high dosages of superplasticizing admixtures have been introduced to meet new demands in design and construction. The predominant requirements for concrete for extremely dense reinforcement (500 to 1000 kg/m3) are high workability (slump of approximately 250 mm) and negligible bleeding or segregation. Concrete mixes fulfilling these requirements and still having a moderate content of cement have been designed by adding 2 percent (by weight of cement) of CSF. Slipform construction and concrete pumping are vital elements in the construction procedures for very large offshore structures. CSF, through extensive full scale field tests and shaft slipforming, has been found to improve the pumpability and stability of high strength/high workability concrete mixes.

Purpose was to study the influence of the length of moist curing time on weight change behavior, chloride ion content, and chloride ion distribution profile through 10 cm concrete cubes made from concretes containing silica fume. Three concretes containing 2.5, 5, and 10 percent silica fume by weight of cement were prepared and tested. The concrete cubes were moist cured for 1, 3, 7, and 21 days. Then, after 21 days of air drying, all the cubes were immersed in 15 percent NaCl solution for 21 days. Following the 21-day soaking period and a subsequent 21-day final air-drying period, chloride ion contents at four different depths were determined using a potentiometric titration procedure. The test results showed that weight gain rate and chloride ion penetration in all tested concretes decreased when the length of moist curing period increased. All tested concretes showed the best performance for both reductions after the maximum moist curing period of 21 days used in this study.

An investigation was carried out to find a suitable additive for acceleration of strength development in blast furnace slag cement at an early stage hydration. Sodium compounds such as NaF, NaCl, NaBr, NaI, NaOH, Na2SO4, and Na2CO3 were used. The strength development, porosity, scanning electron micrographs, and heat liberation characteristics were examined. Addition of a small amount of NaBr, NaCl, NaF, or Na2SO4 increased the strength at early ages; NaBr or NaCl increased the strength even at 91 days. The microstructure of paste with NaBr or NaCl addition showed a structure containing CSH, gel, AFm, ettringite, and other phases having a compact structure.