P.D. Cady

Air content and size distribution of air voids in hardened cement pastes using the section-analysis method

Abstract The section-analysis method was used to determine the air-void parameters of hardened cement pastes. The results are compared to those obtained using the point-count method. Five series of air-entrained cement pastes with different water-to-cement ratios were prepared. The point-count method was conducted using a stereoscopic microscope at 50× and the section-analysis method was applied by taking photographs at 80× and reproducing the surface under study. The air content, specific surface, and spacing factor were determined using the point-count method. The air content and the air-void size distributions were obtained using the section-analysis method. For the size of surface area examined and for the air content tested in this study, the results show that the air contents determined using the section-analysis method are lower than the air contents determined using the point-count method by 1.4% to 34.3%. The air-void size distributions obtained using different calculation procedures compare well to each other for all series.

Photoelastic analysis of rigid inclusions in fresh concrete

Abstract Gelatin was employed to experimentally determine differential settlement stresses in fresh concrete above reinforcing steel. For a 15.9 mm diameter reinforcing bar, the zone of influence and magnitude of the stresses appear to be related to the bar spacing, cover depth, and consistency of the mix. The tensile stresses produced above the reinforcing bars appears to be of sufficient magnitude to produce surface cracking of the concrete and thus may significantly affect the time to corrosion in bridge decks and other similar reinforced concrete structures.

The retardation of reinforcing steel corrosion by alkyl-alkoxyl silane

Abstract The effectiveness of an alkyl-alkoxy silane treatment of concrete on reducing the rate of corrosion of reinforcing steel in the presence of chloride ions was investigated. First, the penetrating characteristics of the alkyl-alkoxy silane into dried concrete were determined. Then, the corrosion currents of 90 corrosion specimens, some of which were dried and silane-impregnated, were measured using an impressed current, accelerated corrosion technique. The penetration of alkyl-alkoxy silane into dried concrete followed an approximate linear square root time relationship. Comparisons of corrosion currents showed that alkyl-alkoxy silane showed that allowing time after treatment for the They also showed that allowing time after treatment for the ethanol carrier to evaporate and exposing the treated surface to water for a short period of time were beneficial.

Compressive strength studies on portland cement mortars containing fly ash and superplasticizer

The effects of two super water-reducing admixtures on the compressive strengths and elastic moduli of portland cement mortars containing fly ash were determined. The results show that the effectiveness of the chemicals for improving the strengths of mixtures in which portland cement is partially replaced by fly ash decreases with an increase in the percentage of ash. Increased strength can be nil or too low to justify the additional expense associated with the chemicals. The mixtures did exhibit normal stress-strain relationships: the elastic moduli were related to the ultimate compressive strengths in the usual manner. The results are based on mixes with equal workabilities.

A chemical approach to the problem of alkali-reactive carbonate aggregates

Abstract This paper presents the results of a laboratory investigation of postulated mechanisms and potential remedial measures involving alkali carbonate reaction in concrete. This reaction involving certain carbonate (limestone) aggregates when used with high alkali cement has resulted in distress (cracking) of concrete pavements and slabs. The observed distress has been attributed to dedolomitization of the aggregates and osmotic pressures. This study was conducted to determine whether a chemical approach to the problem could reduce the expansion to acceptable levels. The results were encouraging. Expansion was reduced by as much as 50% using two common chemical substances, lithium carbonate and ferric chloride, introduced into a high alkali portland cement concrete made with a very reactive coarse aggregate, Gull River limestone from Kingston, Ontario, Canada. Another substance, dimethylsulfoxide, was tested also, with insignificant changes in measured expansion.

A field method for measuring the chloride content of concrete

Abstract A previous laboratory study demonstrated that based on accuracy, cost, speed, and level of expertise, the specific ion electrode was the best method for field measurements of the chloride content of reinforced concrete. This study addresses the development of a field procedure for measuring the chloride content of concrete using the specific ion electrode. The procedure requires a method to extract powdered samples, weigh 3.0 grams of extracted powder and calibration of the specific ion probe. The sampling method uses a vacuum collection, carbide drill sampling unit. Calibrated vials, a low cost scale and a triple beam balance were evaluated as sample weighing devices. The calibrated vials are too laborious and slow and the low cost scale too inaccurate. The calibration method was shown to be quick and consistent with a very small variance independent of number of measurements per specimens and calibration run. Samples taken from three bridges in Florida, Virginia, Pennsylvania and Wisconsin demonstrated that aggregate type has no effect on the chloride measurements. Finally, the variance associated with the instrument and the operational procedures of the test method was determined.

Penetration of concrete with various linseed oil/mineral spirits mixtures

Abstract Field impregnation techniques were simulated in the laboratory using concrete cylinders (different water:cement ratios) dried either in a forced air oven or with a gas-fired infrared heater after which they were impregnated (by ponding) with different linseed oil/mineral spirits mixtures. Mass uptake was obtained for impregnation with various mineral spirits concentrations and impregnation temperatures. Generally as the water:cement ratio, impregnation temperature, and mineral spirits concentration increase, the final mass uptake (or rate of mass uptake) and penetration depth also increase. Further, the infrared dried specimens displayed a deeper final penetration depth than the ovendried specimens. Regression analysis produced equations that predict the final penetration depth in the concrete as a function of percent mineral spirits in the linseed oil mixture.

Residual porosity after impregnation of concrete with linseed oil/mineral spirits mixtures

Abstract Pore characteristics of concrete impregnated with boiled linseed oil were investigated using a mercury porosimeter. Prior to impregnations, specimens were dried either in a forced-air oven or with a gas-fired infrared heater. For impregnation, boiled linseed oil was mixed with various amounts of mineral spirits by weight. As the percentage of mineral spirits increased, the total specimen porosity increased, but the total porosity was still lower than that of the unimpregnated controls. Pore size distrubution shifted with impregnation and varied with the percentage of mineral spirits used. Regression analysis revealed relationships between the total intrusion, percent reduction in porosity, and total porosity versus percent boiled linseed oil by weight.

Impregnation of concrete with hot epoxy resins

Abstract Impregnation of concrete with two types of hot epoxy resins was investigated. Compared with the more commonly used acrylics, epoxies offer reduced danger from fumes, fire and explosion. Economic advantages due to the reduction or elimination of the post-drying cool-down period are also afforded by the epoxy. This study revealed that an aliphatic-based epoxy impregnant at 105°C displays an uptake rate approaching that of acrylic monomers. However, the narrow span between the polymerization and degradation temperatures could limit applicability.

Chloride penetration of concrete impregnated with various linseed oil/mineral spirits combinations

Abstract Concrete test cylinders (3 × 6 in., or 7.6 × 15.2 cm) dried in a forced air oven or with a gas fired infrared heater were impregnated with different boiled linseed oil/mineral spirits mixtures. The impregnated cylinders, along with nonlinseed oil impregnated cylinders, were contaminated with a saturated sodium chloride solution. Chloride content determinations were performed on mortar specimens obtained at various depths from the surface of the cylinders. Chloride contents determined on the controls indicated chloride levels much higher than probably would have occurred in actual field concrete. The data on linseed oil mixture impregnated concrete indicate that chloride ion penetration into the concrete is significantly reduced as compared to the control specimens.