Development of high strength lightweight concrete for structural applications

The use of superplasticizers and mineral admixtures, particularly condensed silica fume, has led to the development of high strength, normal weight concretes for structural applications. The judicious use of these materials has resulted in concrete compressive strengths exceeding 100 MPa.

Notwithstanding the relatively low strength of lightweight aggregates, this investigation reports results of a study undertaken to develop high strength lightweight concretes using a Canadian lightweight aggregate. A series of seven concrete mixtures involving 25 batches were made. The cement, or cements, fly ash and silica fume content of the mixtures ranged from 300 to 635 kg/m³. All mixtures were air entrained and superplasticized. A large number of test cylinders and prisms were cast for the determination of the mechanical properties of concrete and to evaluate its resistance to freezing and thawing cycling, performed in accordance with ASTM C 666 Procedure A.

From the results of this investigation, it is concluded that high strength concretes with densities of less than 2000 kg/m³ can be made with or without the use of mineral admixtures, but the use of superplasticizers is mandatory. The highest compressive strength achieved was 66.5 MPa at 365 days for a cementitious content of 638 kg/m³. The 28-day splitting-tensile strengths obtained were of the order of 3.5 MPa. The freezing and thawing tests performed in accordance with ASTM C 666 Procedure A, freezing in water and thawing in water, indicated excellent frost resistance of concrete with durability factors generally greater than 90.