International Concrete Abstracts Portal

Two different types of latex modifier were used to determine how curing conditions and latex-modifier content influenced compressive strength and durability. Freeze-thaw resistance in the presence of a 2.5 percent NaCl solution was evaluated by measuring both relative dynamic modulus and mass of scaled material. While all specimens were 14 days old at the start of testing, compressive strength increased as the period of initial wet-curing increased, durability factor values (ASTM C 666) were insensitive to the period of initial wet-curing, and scaling resistance was improved by increasing the wet-curing time. The air-void system, described by the spacing factor, was found to have a greater influence on durability and scaling than either latex-modifier content or duration of wet cure. A control mix made using a high-range water-reducing admixture (HRWRA) was used as a basis of comparison.

The key to casting high-strength concrete with compressive strength of more than 100 MPa into complicated reinforced structures is to give the concrete high fluidity as well as to improve strength. The authors developed an acrylic copolymer-based new superplasticizer that can improve fluidity of concrete with water-binder ratio of around 0.20. Paper presents results of a series of studies conducted to determine the properties of fresh and hardened high-strength concrete using the newly developed superplasticizer. The effect of the new superplasticizer was examined with varying water-binder ratio, type of cement, and temperature compared with conventional superplasticizers. The new superplasticizer needed a much lower dosage than conventional superplasticizers to attain a certain slump (250 mm) for a water-binder ratio of around 0.20, and it significantly reduced concrete viscosity. Sufficient workability was kept for 2 hr without much delay in setting time, while conventional superplasticizers showed large slump loss and excessive delay in setting time. Results of strength development, drying shrinkage, and freeze-thaw resistance did not show any harmful effect. Field studies were conducted on application of the high-strength concrete to a prestressed concrete bridge with design strength of 100 MPa using the new superplasticizer. Workability and strength development of concrete were tested and resulted in sufficient quality.

Reports the results of an experimental research program on polypropylene fiber reinforced cement mortars. The purpose of the work was to define the effects produced on a basic mortar by addition to the mixture of various synthetic polymers in the form of latexes. The significant features considered that characterize a cement mortar formulated for repairing concrete structures include workability, low permeability, dimensional stability, mechanical resistance (compressive and flexural strength), Young's modulus of elasticity, ductility, toughness, and durability. The test results suggest that optimal characteristics have been obtained (given a minimum percentage of fibers) with a content of 10 percent silica fume by weight of cement and by using acrylic acid copolymer water dispersion at the rate of 9 percent of the solid polymer to cement. For protective use, it is possible to modify the basic mortar by a styrene-butadiene copolymer water dispersion; however, the modification of the basic mortar by using styrene-acrylic polymer latex generates a product suitable either for repairing or coating of reinforced concrete structures. The reliability of this last modified mortar as a protective coating has also been investigated. The most significant results relate to the penetration of Cl- and SO 4-ions, variation of bond strength between mortar and concrete, and effectiveness of a thin layer of such a cement composite, correlated to rate of steel corrosion. Equivalent criteria have been described comparing different mortar covers, with the minimum cover thickness of concrete as prescribed by European codes, by using an electrochemical test procedure.

Paper addresses shrinkage and cracking at early ages of highly flowable flowing concrete with a special admixture (unit amount of water of 185 kg/m 3) and of normal high-strength, viscous concrete with high-range AE water-reducing agents (unit amount of water of 170 kg/m 3) under constant air flow. Results are as follows: 1) shrinkage at early ages of flowing concrete and normal high-strength concrete increased with a decrease in water-cement ratio. Shrinkage of normal high-strength concrete varied according to the admixture composition; 2) cracking of both flowing concrete and normal high-strength concrete within a restricting steel frame initiated at an earlier age and became significant with decreasing water-cement ratio. Time and amount of crack initiation of normal high-strength concrete varied according to admixture composition.

Flowing concrete is characterized by high flowability, requiring only slight consolidation by vibrating and easy control in a plant. An experimental model structure using flowing concrete was made. Paper deals with placing capability on site and properties of hardened flowing concrete in the structure. Pumpability, flowability, and capability to fill forms were investigated for the fresh flowing concrete, and distribution of compressive strength, carbonation depth, cement content, air permeability, and water absorption were measured. Compressive strength of core samples taken from the model structure and standard cylinder specimens from the plant mixture were approximately 24 Mpa. The average estimated cement content was 333 kg/m 3 and the standard deviation was 15 kg/m 3 within a wall of 3 x 4.2 m. Measured carbonation depth was smaller in the freely flowed portions than in the upper portion of vibrated parts.