International Concrete Abstracts Portal

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.

Flowing concrete with high flowability prepared with river gravel and crushed stone was investigated for mix proportioning, flowability, strength, shrinkage, carbonation, and freeze-thaw resistance. This concrete has proved highly feasible in terms of cost and performance. The main findings can be summarized as follows: 1) the slump of flowing concrete is capable of sufficiently filling with slight compaction ranges of 24 to 26 cm, corresponding to a flow from 50 to 60 cm, and a differential height less than 8 cm in the box test; 2) flowing concrete with a water-cement ratio from 30 to 60 percent can be made by using a new admixture and with a simple correction of the standard table of mix proportioning; 3) flowing concrete can be produced with specified concrete strengths ranging from 18 to 60 MPa; 4) strength and durability of flowing concrete showed no significant difference from that of AE concrete without any special admixtures.

The impact of superplasticizers and water-soluble polymers, i.e., rheological modifiers, on the rheology and performance of cement-based systems has been investigated. Combinations of water-soluble polymers and superplasticizers can be used to formulate grouts, mortars, and concretes with properties tailored for specific applications. Cement-based systems studied ranged from highly fluid injection grouts to cohesive, flowable concretes suitable for underwater construction and repair applications. Paper demonstrates how the rheology and performance characteristics of cement-based systems can be manipulated using superplasticizers and rheological modifiers. Specifically, the performance properties of a high-molecular-weight polysaccharide produced to fermentation are compared and contrasted with cellulose derivatives. Combinations of water-soluble polymers and superplasticizers can be formulated to produce a continuum of properties ranging from highly fluid, nonseparating grouts to low-slump concretes with enhanced workability and water retention. Choice of the proper combination of superplasticizer and water-soluble polymer is determined by the functional demands of each application.