International Concrete Abstracts Portal

This paper reports on part of a substantial research programme on properties of condensed silica fume (CSF) concretes cured in temperate and climates, carried out in the Department of Civil Engineering at Loughborough. The hot The research approach was to investigate mixtures proportioned to have equal workability and 28 day strength (when water cured at 20°C). This paper examines the effect of superplastizer, curing method (water and polythene) and curing environment (temperate and hot) on the compressive strength, permeability and pore structure of 40 MPa concretes. More specifically, the paper contrasts the performance of two 15% CSF mixtures (replacement by weight of cement) where workabilities were controlled by the addition of extra water or superplasticizer. The development of the concretes’ strength and subsurface permeability index (air and water) with age (from 7 to 180 days) is described, together with the intrinsic permeability (air and water) and pore structure of their equivalent mortar fraction. The use of superplasticizer to control workability increased the compressive strength of CSF concrete mixtures by around 18% and 10% in the temperate and hot environments respectively. The super-plasticized concrete had lower air and water permeabilities which is attributed to an improved pore structure as confirmed by mercury intrusion porosimetry date. The improvements were more marked in the CSF concretes cured in a hot environment.

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.

High-strength concrete with air-entraining high-range water-reducing admixture, 0.35 water-cement ratio, 148 kg/m 3 unit water content, and about 60 MPa compressive strength, was produced, and the admixture content and sand percentage were varied. The consistency property was measured by the slump test, and the compaction property and segregation resistance were determined by the flow time through an inverted slump cone. An appropriate mixture that balanced these properties relative to the admixture content and sand percentage was determined from the test. The appropriate mixture can be consolidated by using a shorter vibrating time and lower frequency than in the case of ordinary concrete.

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.

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.