[27] Development of high strength lightweight concrete for structural applications H.S. Wilson, V.M. MalhotraThe 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/m3can 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.

[28] Strength and deformation of lightweight concrete of variable moisture content at very low temperaturesF.S. Rostsy,U. PuschThis paper deals with the influence of very low temperature cycles on strength, deformation and thermal strain behaviour of structural lightweight concrete. The tests were performed on concrete with a strength of about 45 MPa. The results show that the mechanical properties of this concrete at low temperatures are strongly dependent upon the moisture content of the paste matrix and porous aggregate. Irreversible thermal expansion occur after return to room temperature, if the moisture content of concrete is high. Cylinder strength, tensile splitting strength and modulus of elasticity in compression increase with falling temperature. Lightweight concrete with a high moisture content and subject to temperature cycles suffers a great loss of compressive and tensile splitting strength.

[29] Compressive strength evaluation of structural lightweight concrete by non-destructive ultrasonic pulse velocity methodABSTRACTIn this paper the compressive strength of a wide range of structural lightweight aggregate concrete mixes is evaluated by the non-destructive ultrasonic pulse velocity method. This study involves about 84 different compositions tested between 3 and 180days for compressive strengths ranging from about 30 to 80MPa. The influence of several factors on the relation between the ultrasonic pulse velocity and compressive strength is examined. These factors include the cement type and content, amount of water, type of admixture, initial wetting conditions, type and volume of aggregate and the partial replacement of normal weight coarse and fine aggregates by lightweight aggregates. It is found that lightweight and normal weight concretes are affected differently by mix design parameters. In addition, the prediction of the concrete's compressive strength by means of the non-destructive ultrasonic pulse velocity test is studied. Based on the dependence of the ultrasonic pulse velocity on the density and elasticity of concrete, a simplified expression is proposed to estimate the compressive strength, regardless the type of concrete and its composition. More than 200 results for different types of aggregates and concrete compositions were analyzed and high correlation coefficients were obtained.