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Compressive strength of concrete with silica fume cured at high temperatures generated by heat of hydration during early age was studied. The curing temperatures simulated the site-curing conditions of structural members. Four types of aggregates and four types of admixtures were used, and a total of seven concrete samples were cured at four temperature conditions ranging from 20 to 75 C. Results indicated the following: 1) at higher curing temperatures, the 1-week strength was higher but the strength gain from 1 to 4 weeks tended to be low; 2) independent of curing temperature, the type of aggregate greatly influenced the strength, and the results were the same with all the admixtures; 3) high-temperature curing influenced concrete strength independently of the admixture and aggregate; 4) equivalent age at 20 C based on the Arrhenius equation gave a reasonable estimation of compressive strength gain.

Class F fly ash was used as the basic granulating material. Catalysts and binders were added to evaluate the behavior of granulated material. The accelerated curing method was also considered. Results indicate that granulation rate depends closely on the slant angles of the disc, the revolving rate, the methods of adding admixtures, and granulation time. Though aluminum powder reduced unit weight and raised the strength of fresh particles, it had a detrimental effect on other properties. Addition of hydrophilic seed reduced the granulation time and increased productivity. The results showed that at a constant relative humidity, the higher the temperature, the more rapid and higher the strength development. It is important to maintain constant temperatures or low strengths may result. Normal steam curing, autoclave curing, and microwave steam curing have beneficial effects on the strength of fly ash lightweight aggregates. The differences in curing results are due to differences in mix proportioning of aggregates and duration of curing.

High-lime fly ashes obtained from the combustion of lignites or subbituminous coals are common by-products of thermal power plants in many countries, including Turkey. Chemical analyses, mineralogical analyses, and the formation of hydration and pozzolanic reaction products at different ages of three Turkish high-lime fly ashes were carried out using X-ray diffraction (XRD) techniques. The relationships between the mineral phases in the fly ashes and the hydration and pozzolanic reaction products were investigated. Fly ash is formed at combustion temperatures of approximately 1000 C, at which the clay impurities decompose. These fly ashes contained highly reactive silica and alumina. The reaction of these oxides with the free lime and anhydrite present in two of the fly ashes led to the formation of C-S-H gel and ettringite starting with the beginning of hydration. The third fly ash, having anhydrite as the only major calcium-bearing compound, produced gypsum upon hydration. However, introduction of Ca(OH)2 into the system resulted in similar reaction products. At later ages, beside the previously mentioned products, C4ACH11 and C4AH13 were also observed in all three cases. Interpretation of the results indicated that although all three fly ashes were of high-lime type, two of them were hydraulic and autopozzolanic, whereas the third was pozzolanic only.

The admixtures of condensed silica fumes (CSF) and phosphogypsum (neutralized and dehydrated at 400 C) were used together with fly ashes as blended cement components to improve early strengths and other properties. The cements with the initial 15 to 50 percent low-calcium PFA content (SiO2 + AL2O3 + Fe2O3 - 83.3 percent) or 15 to 70 percent high calcium PFA content (22.1 percent CaO) were mixed with the additional components just mentioned. Standard tests at normal curing were made, as well as measurements after the low-pressure steam treatment at 70 C. All cements mixed with CSF showed standard compressive strengths about 13 to 20 MPa higher than the reference mortars. More detailed studies of the hardening process were also carried out using calorimetry, DTA, TG, XRD, and porosimetry, which showed acceleration of the hydration process due to pozzolanic properties of CSF. Reduction of total porosity and pore size was also found. The same positive effect of CSF was observed in the case of mortars treated at 70 C. This additive improves significantly the pozzolanic properties of low-calcium PFA. At standard curing, activated phosphogysum addition brings about a decrease in the hydrated calcium silicates. A substantial amount of ettringite forms and partially inverts into monosulfate after 28 and 90 days of hardening. At accelerated curing, the mortars containing phosphogypsum show a significantly higher degree of hydration than the reference mortar. The results relating to pastes and mortars have been confirmed for concretes. Therefore, one can conclude that the admixtures studied, particularly CSF, have positive influence on the properties of PFA concretes and help to augment the effect of PFA content in these concretes.

The anchorages of Akashi Kaikyo Bridge are mass concrete having horizontal dimensions of 60 x 85 m, and a height of 45 m. Precooling and pipe cooling of concrete are used to prevent the thermal cracking of these mass concretes. Furthermore, the low-heat cement has been judged to be more effective to reduce the occurrence of thermal cracks. Comparisons have been made of the basic properties of concrete using a variety of low-heat generating cements to select the ones suitable for the project. The new types of low-heat cement have different ratios of finely ground blast furnace slag, fly ash, and portland cement, and can be broadly divided into binary blended types containing large quantities of slag, and ternary blended types containing large quantities of slag and fly ash. Paper gives results of the strength and adiabatic temperature rise in concrete made using these low-heat-type cements, and the influences of the slag and fly ash on the properties of concrete are described. Although low-heat-generating concrete generally shows retardation in the setting time and shows more bleeding, it was found that the use of very finely ground blast furnace slag and finely ground limestone powder improved workability of concrete, reduced bleeding, and is effective for the development of early-age strength.