Achieving high strength/high performance concrete from coral-limestone aggregates using ordinary Portland cement, fly ash and superplasticizer

Abstract eng:
In Dar es Salaam city, Tanzania, most high rise buildings and bridges are constructed using granite aggregates which are hauled from about 120  km away and this becomes very expensive. Most engineers are reluctant of using the coral limestone aggregates found around the city, and which are plenty, because of the feeling that concretes produced from such aggregates may not meet the strength and durability requirements given in the standards. Investigations were carried out on the quality of concretes made of different mixes using the coral limestone aggregates found around with class 42.5 R Portland cement partly replaced by 0%, 10% and 20% fly ash. The mix design was done according to the British (DOE) method. A water cementitious ratio of 0.3 was maintained throughout. A superplasticizer with a brand name Mega-Flow SP 102 was used to enhance the workability of the concrete mixes. Tests were carried out on concrete cubes at 7, 28 and 56 days. Results gave mean compressive strength values of about 50 MPa after 56 days for all replacement ratios. The maximum strength achieved was limited by the strength of the aggregates as failure occurred in the aggregates before failure of the mortar. Tests at 28 days on the rate of water penetration with 20% replacement of fly ash using a concrete impermeability tester gave a value of 9.8 × 10−5 mm/sec which falls in the range of low permeability category according to ISO/DIS 7031. The conclusion which can be drawn from these investigations is that it is possible to produce a durable concrete with a mean strength of 50 MPa using the coral limestone aggregates found in Dar es Salaam.

• Export as: BibTeX | MARC | MARCXML | DC | EndNote | NLM | RefWorks
• Add to your basket