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Results of an experimental investigation performed to evaluate the effect of various concrete strength levels on behavior of lightweight concrete (LWC) under pure torsion are reported.The principle variable of the testing program was compressive strength of concrete (�'c) which ranged between 6.9 and 81.4 MPa. Ten mixture proportions were utilized for LWC of 1500 to 2050 kg/m3 unit weight. In total, sixty four (thirty two pairs) rectangular specimens with 100x 200 mm cross-section were tested. Ultimate torsion strength of LWC increases as uniaxial compressive strength increases however the increase rate reduces for high levels of concrete strengths. The test results are compared with predictions of elastic and plastic theories for torsion and the ACI Code. The Code underestimates the cracking torque of LWC under pure torsion. A regression equation incorporating test results is higher than the ACI equation prediction by a factor of 1.12.

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Self-desiccation is the major source of autogenous shrinkage and crack formation in low water-binder ratio (w/b) concretes

which can be reduced by internal curing. In this paper performance of high strength self consolidating concrete (HS-SCC) with

w/b of 0.28 and 0.33 including autogenous shrinkage, drying shrinkage, compressive strength, and resistance to freezing-thawing

was investigated. Then, for the purpose of internal curing, 25% of normal weight coarse aggregate volume was replaced with

saturated lightweight aggregate (LWA) of the same size and its effects on the material properties was studied. Two modes of

external curing, moist and sealed, were applied to test specimens after demoulding. Autogenous shrinkage from 30 minutes to 24

hours after mixing was monitored continuously by a laser system. The initial and final setting time were manifested as a change

of the slope of the obtained deformation curves. Shrinkage after initial setting was 860 and 685 microstrain (&mu&epsilon) for 0.28 and 0.33

w/b mixtures, respectively. The saturated LWA reduced these values to 80 and 295 &mu&epsilon, respectively. By LWA Substitution the 28-

day compressive strength of 0.28 w/b mixture was reduced from 108 to 89 and 98 to 87 MPa for moist and sealed cured specimen,

respectively. The corresponding values for 0.33 w/b mixture was 84 to 80 and 82 to 70 MPa. Shrinkage of 0.28 w/b mixture

without LWA after moist and sealed cured specimen dried for 3 weeks was about 400 &mu&epsilon. Shrinkage of moist and sealed cured

specimen containing LWA was reduced 9% and 25%, respectively. On the contrary for 0.33 w/b mixture an increase was noticed.

Freezing-thawing resistance was improved by sealed curing, decreasing w/b and substituting LWA.

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This paper aims to characterize the elastic modulus of structural modified normal density (MND) and lightweight aggregate concrete (LWAC) produced with different types of expanded clay lightweight aggregates (LWA). A comprehensive experimental study was carried out involving different concrete strengths ranging from 30 to 70 MPa and density classes D1.6 to D2.0. The influence of several factors on the LWAC elastic modulus, such as the cement content, initial wetting conditions, type and volume of coarse LWA and the partial replacement of normal weight coarse and fine aggregates by LWA are analyzed. The strength and deformability of LWAC seems to be little affected by the addition of high reactive nanosilica. Reasonable correlations are found between the elastic modulus and the compressive strength or concrete density. The obtained LWAC elastic moduli are compared with those reported in the literature and those estimated from the main normative documents. In general, codes underestimate the LWAC modulus of elasticity by less than 20%. However, the MND modulus of elasticity can be greatly underestimated. In addition, the prediction of LWAC elastic modulus by means of non-destructive ultrasonic tests is studied. Dynamic elasticity modulus and ultrasonic pulse velocity results are reported and high correlated relationships, over 0.95, with the static modulus are established.