International Concrete Abstracts Portal

Results of a laboratory test series are reported concerning the effect of cement type, class of fly ash, and fineness of fly ash on the strength development of mortars. Thirty percent by weight of portland cement was substituted by fly ash. The following materials were used in various combinations: Type I and Type III portland cements, Class F fly ash before and after grinding, Class C fly ash before and after grinding, a silica fume, a superplasticizer, and an accelerating admixture. More than 60 different compositions were tested in all. Standard flow, compressive strength, and pulse velocity measurements were performed in the standard manner at 1, 7, and 28 days. The obtained results show the effects of fineness of fly ash, along with other characteristics of mortar composition, on the flow and strength development, as well as the interactions between fineness and cement type. For instance, as expected, ground Class F fly ash with Type I cement produced lower strengths at 1 day than the same fly ash with its original fineness and Type III cement; however, at 7 and 28 days, the fly ash mortars with Type I cement showed higher strengths. The results of the pulse velocity tests showed the same trend as the strength results.

Recently, in Japan, application of the roller compacted dam concrete (RCD) method has increased in the construction of concrete gravity dams. The concrete for the RCD method (RCD concrete) features a very stiff consistency with low water content, which enables the use of a vibration roller for compaction. Most of the cement used so far for RCD concrete has used a combination of fly ash with moderate heat portland cement. However, the supply of high-quality fly ash for use in concrete has recently lessened in Japan. One admixture replacing fly ash is granulated blast furnace slag. In this study, properties of RCD concrete made with slag cement featuring blends of moderate heat portland cement and granulated blast furnace slag were examined. The effect of fineness of the individual slag cement components on compressive strength and adiabatic temperature rise were studied. The unit cement content in the concrete was 120 kg/m 3. The maximum size of the coarse aggregate was 150 mm. The results show that concrete with moderate low-heat slag cement can provide the same or better performance as fly ash cement concrete by employing a rational combination of fineness and slag content. Also, the advantages of slag cement at longer ages were confirmed. The results obtained in this study are now being applied to an actual dam construction.

A reliability-based approach is used to recommend allowable edge loads for precast hollow core slabs. Full-scale test results are used to predict the statistical parameters of the resistance at the edge. The study indicated that the allowable load is a function of dead-to-live load ratio and concrete strength. The analysis is extended to include system reliability of the whole slab due to different failure modes. The failure modes include flexure at midspan and total shear at the ends, in addition to local failure at the edge. The system modeling is composed of a series system made up of three partially correlated elements. A numerical example is also included for illustration. The approach will help engineers make a rational selection of allowable edge loads that occur around large floor openings.

Describes the results of inspection of concrete operations and quality control of concrete at the Valley Bridge Project in Bluffs, Illinois, using a computer model, the CQC REPORT. The following variables affecting potential durability and strength of concrete in bridge structures were evaluated: accuracy of measuring of concrete materials, state of control and capability of batching operations, variations in SSD quantities of ingredients per cubic yard of concrete, yield, control over the water-cement ratio, properties of freshly mixed concrete, age of concrete at discharge, compressive strength of concrete cylinders, standards of control over concrete manufacture and concrete testing, amount of rejected concrete, and reason for rejection. Paper is concerned with the 6000 psi (41.4 MPa) concrete mix supplied for bridge spans from one of two batch plants used on the job. Paper also describes the structure of the CQC REPORT and statistical techniques used to analyze test data.

The Bureau of Reclamation has proportioned roller compacted concrete (RCC) mixtures since 1979, beginning with the Upper Stillwater Dam Project. Reclamation's research and project-related RCC investigations cover a variety of structures and varying site conditions. Reclamation proportions RCC mixtures to meet both fresh and hardened concrete properties. This assures construction of high-quality concrete structures. Ongoing research has continued to identify specific properties of RCC, such as bond strength, freeze-thaw durability, and thermal properties that significantly affect the performance of these structures. Paper summarizes RCC mixture proportions and properties of fresh and hardened concrete from Reclamation's RCC research and project activities.