International Concrete Abstracts Portal

Concrete placed in contact with a sulfate environment can severely degrade due to formation of expansive compounds such as ettringite. The use of low-calcium fly ashes in concrete have been successful in mitigating these expansions. However, some high-calcium ashes have the potential to cause increased expansion of the concrete, leading to accelerated deterioration. This research focuses on producing cements interground with Class C fly ash, which can be used to produce sulfate-resistant concrete. ASTM Type I and Type II cements were blended with a sulfate-susceptible Class C ash in amounts from 0 to 70 percent fly ash. Concrete was produced using a standard Texas Highway Department 306 kg/m 3 mixture and the various interground and unblended cements. Specimens were soaked and monitored monthly for 3-1/2 years in a 10 percent sodium sulfate solution to accelerate sulfate attack. Results indicate that certain specimens made with interground cements having fly ash contents between 25 and 70 percent, and additional blended gypsum, achieved lower expansion than control specimens made with Type II, Type V, or 0 percent C 3A cements alone. This was true for fly ash/cement blends using both Type I and Type II cements. Compressive strengths of the fly ash blends, through 365 days, attained levels generally comparable to, or better than, the controls.

In the present research project, fly ash was mechanically processed to 1 to 5 micron particle size. Mortars and concretes were made from these processed fly ashes. In this paper, the results of the micronized fly ash are compared to the results gained with air classified fly ash, silica fume, and blends. It was found that using ground fly ashes, very fluid mixtures can be produced with excellent strength and durability properties. Because of the growing interest in ultra-fine supplementary cementing materials (SCM's) for high-performance concrete, there is a need to find ways to micronize fly ashes in an economical way.

Presents an adaptation of a previous model (the generalized Feret's law with account for the Maximum Paste Thickness) for structural fly ash concrete. A kinetics term is introduced to predict the compressive strength development between seven and 365 days. On a set of data taken from the literature, the mean accuracy of the model is equal to 2.1 MPa. Moreover, the formula only incorporates a limited number of parameters, which can easily be determined from standard mortar or concrete tests. Therefore, the model appears to be suitable for a computer-aided concrete proportioning software.

Describes the performance of a cement-based grout recommended for possible use to control brine inflows in potash mines. The grout consists of Type III high-early-strength cement, fly ash, and sodium saturated brine. Specimens were prepared and submerged in containers filled with brine to cure under confining pressures of 0, 3.40, and 6.9 MPa (0, 500, and 1000 psi). The isotropic confining pressures were designed to simulate different mining environments and to accelerate penetration of brine into the specimens so that long term performance could be evaluated. Tests were conducted at different ages to determine the compressive strength, splitting tensile strength, and static and dynamic modulus of elasticity. The performance of grout mixtures containing brine with zero and 40 percent fly ash over the three-year test program seems to be in an acceptable range. Confining pressure can adversely affect the physical properties results of grout over time. This investigation found that a reduction in the physical properties was occurring after two years, especially when the grout was subjected to a confining pressure. The grout with fly ash exhibited a more scattered data under different confining pressures than grout with no fly ash; however, it showed a better long term performance. Generally, fly ash grouts stored under zero confining pressures were found to perform better than those subjected to high confining pressures.

As part of a series of experiments designed to develop binary and ternary blended cements for use in structures exposed to freezing and thawing cycles in the presence of deicer salts, 39 mortar mixtures were made. Five different portland cements (two Canadian Type 10 cements, two ASTM Type I cements, and one Canadian Type 30 cement), seven fly ashes (three Class F fly ash, one Class CF fly ash, and three Class C fly ash), and two blast furnace slags were used as cementitious materials. The water-cementitious material ratio of all mixtures was fixed at 0.40; the amount of supplementary cementitious material (as a percentage of the total mass of binder) was zero percent for the five portland cement reference mixtures, 20 percent for nine mixtures, and 40 percent for the other 25 mixtures. The compressive strength of all mortars was measured after seven, 28, and 90 days of curing in water. The pore size distribution (with mercury intrusion porosimetry) and the chloride ion permeability of all mortars were determined after 28 days of curing. The results of the tests carried out to analyze the portland cements, the fly ashes, and the slags are also given in this paper. It was found that certain mixtures containing 40 percent of supplementary cementitious material had an excellent 28-day strength, a very low chloride ion permeability, and a very small average capillary pore size.