Aggregate-cement Ratio Research Articles

Considerations for Potential Use of Nuclear DensityGages on Concrete

The principal purpose of this study is to decide if the potential use of nuclear density gages to estimate concrete density might produce results worthy of accurate engineering interpretation. As such, it was important to verify the degree to which the proportions of mix components affect the interrelationship of density, air content, and compressive strength of concrete in order to establish lish the precision of concrete density estimate required to determine in situ air content or predict potential compressive strength. Once this required precision was found it was compared briefly with the precision to be expected of standard industry nuclear density gages. An extensive testing program was carried out that covered a wide range of water-cement ratios w/c and aggregate-cement ratios a/c. Results indicate that if a nuclear density gage can measure the density of concrete to within plus or minus 1% (a value that such a device should be capable of), then the air content and compressive strength of that concrete can be estimated to within an acceptable range.

Optimization of Concrete Mis Proportioning Using Reduced Factorial Experimental Technique

A method of optimizing concrete mix proportioning for a given workability and compressive strength using factorial experimental technique is described. The experiments were designed to consider the simultaneous variations of the controlling factors, namely water-cement ratio, aggregate-cement ratio, and course-total aggregate ratio in such a way that the various combinations of these factors would yield mixes in the practical ranges of workability and compressive strength. The aim was to reduce the number of test mixes and specimens without sacrificing the accuracy of evaluation of the effects of variation of these factors on the workability and compressive strength.

Use of pulse velocity to predict compressive strength of concrete

Prediction of compressive strength of concrete at 28-days and 63-days from pulse velocity at 1-day and 3-days is shown. The prediction is made by using pulse velocity and other variables such as water-cement ratio, aggregate-cement ratio, coarse aggregate-sand ratio, amount of cement in the mix, slump, flyash content, and vebe time.Simple regression was used and carried out by a statistical computing system called Minitab. Typical relationship between pulse velocity and compressive strength, and pulse velocity and other variables are also given.Mix properties proved to be very important in the regression process and showed improvement in the results when used with pulse velocity.

Technical notes: Strength characteristics of laterite-cement mortars

The abundance of lateritic soil deposits in Nigeria has led to some applied research studies on this material. The major aim has been to promote the judicious utilisation of laterite in the construction industry. The influence of clay portion of lateritic soils, water-cement ratio, and aggregate-cement ratio on the compressive strength of laterite-cement mortars was investigated in this study. The results show that clay impairs the strength of laterite-cement mortars, and that for some mix proportions, the strength compares favourably with that for the standard sand-cement mortars. It was also found that laterite-cement mortars could be designed for strength ranging from below 1 N/mm 2 to about 30 N/mm 2.

Recycled Concrete—A Source for New Aggregate

Abstract Recycling concrete rubble as aggregate material for the construction programs in the Middle East, where high-quality mineral aggregate is scarce, offers an excellent ecological and economic opportunity. Based on tests carried out on 21 mixes, this investigation attempts to develop data especially on the strength, failure mechanism, and durability characteristics of the recycled aggregate in comparison with the conventional concrete. Results show that for a W/C ratio of 0.35 the recycled aggregate concrete has 30% lower strength than conventional concrete. The strength differential narrowed for increasing values of W/C ratio until the strengths were about equal for a W/C ratio of 0.55. No significant increase in the strength of recycled aggregate concrete was obtained by reducing the W/C ratio below 0.40. It is indicated that the quality of recycled aggregate concrete will improve with the quality of recycled mortar or if the recycled material has a high aggregate-cement ratio. The recycled aggregate concrete showed somewhat better workability characteristics than conventional mixes although its modulus of elasticity and durability characteristics were lower. It is proposed that satisfactory concrete can be made by recycling concrete as aggregate where disposal problems exist or where natural aggregate is either inaccessible or of inferior quality.

The Electrical Resistivity of Concrete with Emphasis on the Use of Electrical Resistance for Measuring Moisture Content

Abstract The paper describes an investigation of the electrical resistivity of concrete. In particular, electrical resistance of concrete was found to increase with decreasing water-cement ratio and increasing aggregate-cement ratio and entrained air content. The results show that calculating a water-concrete ratio by volume provides a convenient way of comparing the electrical resistivity of concretes of different mix proportions. The study also demonstrates that electrical resistance can be used to measure the moisture content of concrete. Electrical resistance increases as moisture content decreases with the least rate of change within the highest range of moisture contents. Although other techniques for measuring moisture content of concrete are more accurate, the use of electrical resistance has the advantage of being a relatively simple procedure that uses inexpensive equipment.

Properties of laterite aggregate concrete

The paper presents the results of tests conducted on fresh and hardened concrete using laterite as aggregate. Several mixes of laterite aggregate concrete were made with varying watercement and aggregate-cement ratios to study the properties like workability, compressive, flexural, tensile strength and Modulus of elasticity. The tests indicate that the workability decreases with increasing aggregate-water ratio. The compressive strength of laterite aggregate concrete is considerably lower than that of gravel or crushed granite aggregate concrete, while the average ratio of cylinder to cube strength compared favourably with that for normal aggregate concrete, for the range of aggregate and water-cement ratios covered in this investigation.

Workability of gap-graded versus continously-graded concrete and the correlation of slump with Vebe time

The workability of both gap-graded and continuously-graded concretes of various mixture proportions has been measured concurrently by the slump of a standard cone and by a Vebe consistometer. The results are compared for both concretes on the basis of equal maximum size of coarse aggregate, water-cement ratio, and aggregate-cement ratio. The comparison has shown the relative ease of placing gap-graded concrete to attain uniform compaction. Based on test data, a comparative study of the efficacy of slump test versus Vebe time as a measure of workability has been made. The slump test is not fully indicative of the workability for stiffer mixtures with slump less than one inch (2.54 cm) which should be normally used for obtaining economical high-strength concrete. It further indicates that the Vebe consistometer should be used, instead, in all stiff mixtures.

Dynamic properties of hardened paste, mortar and concrete

The dynamic moduli and the damping properties of hardened paste, mortar matrix and concrete prisms excited in the fundamental longitudinal, flexural and torsional vibrations are presented. The effects on dynamic properties of curing conditions, water-cement and aggregate-cement ratios, the type of aggregate, mode of vibration and of the presence of rigid inclusions in a relatively soft matrix are investigated. The stress-strain behaviour and the mechanism of damping of cementitious materials are discussed. Relations between dynamic moduli and strength, between damping capacity and compressive strength, and between dynamic moduli and the properties of the constituents are presented.

Behavior of Concrete in Biaxial Compression

The behavior of concrete in biaxial compression is briefly described as determined from experiments performed on six mixes by a testing machine capable of loading concrete slabs simultaneously in two orthogonal directions. Strain readings in the three principal directions, microcracking, and ultimate load were observed and measured for various values of lateral load on specimens from each mix. The results show that the elastic parameters, the load at which microcracking occurs, and the ultimate load are not constant but are dependent on the value of the lateral load. The effect of varying the aggregate size, water-cement ratio, and aggregate-cement ratio was also studied; these were shown to have a considerable influence on the properties of concrete in biaxial compression.