Mechanical Properties and Durability of Superplasticized Semi-Lightweight Concrete

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Title: Mechanical Properties and Durability of Superplasticized Semi-Lightweight Concrete

Author(s): V. M. Malhotra

Publication: Special Publication

Volume: 68

Issue:

Appears on pages(s): 283-306

Keywords: age-strength rela durability; flexural strengt high-strength concretes; lig cretes; manufacturing; ion; ; fl twei compressive y ash; freez ght aggregat strength; concrete e-thaw durability; es; lightweight con-mix

Date: 1/1/1981

Abstract:
This investigation was undertaken to determine whether or not the use of superplasticizers can help in the manufacture of semi-lightweight concrete having compressive strengths in excess of 30 to 40 MPa at early ages. Further, the investigation was extended to find if the combined use of superplasticizers and fly ash can produce high strength concrete with moderate cement contents. Three series of concrete mixtures were made using normal portland cement, lightweight coarse aggregate and natural sand. All mixtures were air-entrained and superplasticized except the con-trol mixture which was only air-entrained. In the four mixtures of Series A, cement content ranged from 406 to 443 kg/m3, and test cylinders and prisms were used for strength and durability studies. In the three mixtures of Series B, cement content ranged from 422 to 445 kg/m3, and test cylinders were used for strength determination only. In the two mixtures of Series C, part of the cement was re-placed by fly ash and test cylinders and prisms were cast for the determination of compressive and flexural strengths. The investigation revealed that the use of superplasti-cizers allows the manufacture of semi-lightweight concrete having compressive strengths of the order of 30 and 40 MPa at one and three days respectively. The unit weight of the fresh concrete ranged from 1835 to 1961 kg/m3. In the durability test, the appearance of the test prisms was characterized by a number of aggregate popouts after 300 cycles of freezing and thawing; in one instance, these became numerous after 400 cycles. Notwithstanding the above, the changes in the length of prisms after 400 to 500 cycles of freezing and thaw-ing were well within the accepted limit of 0.07 per cent and the relative durability factors were greater than 99 per cent. It was indicated that the combined use of superplasti-cizers and fly ash can produce high strength semi-lightweight concrete at moderate cement contents. Compressive strengths of 47.6 and 50.7 MPa at 28 and 365 days were obtained for concrete with cement and fly ash contents of 393 and 60 kg/m3 respectively.