Purpose
– This paper aims to assess the suitability of cement combination containing CEM I, fly ash, silica fume and metakaolin for durability design against carbonation-induced corrosion in concrete.
Design/methodology/approach
– Cube compressive strengths at 28 days and accelerated carbonation depths at 28 days and at various exposure ages were determined at the water/cement ratios of 0.35, 0.50 and 0.65. To assess their suitability for carbonation-induced corrosion, the material costs and embodied carbon dioxide (eCO2) contents of the concretes at equivalent performance were compared.
Findings
– Cement combination concretes achieved equal carbonation resistance with CEM I at higher compressive strengths, lower water/cement ratios and higher cement contents. The comparison of the concretes, at equivalent performance, based on the carbonation-induced corrosion exposure classes XC3 and XC4 (Table A.4 of BS 8500-1), shows that ternary and more binary cement concretes have lower costs and eCO2 contents than those recommended in Table A.6 of BS 8500-1.
Research limitations/implications
– This analysis is limited to a working life of 50 years. Further research is needed to verify the suitability of the cement combinations for a working life of 100 years and for the other aspects of durability design covered in BS 8500.
Practical implications
– Cement combination concretes have lower eCO2 content. Hence, when they are cheaper than CEM I concrete at equivalent performance, they would make concrete construction more economic and environmentally compatible.
Originality/value
– This research suggests the inclusion of metakaolin and ternary cement combination concretes in BS 8500 for durability design against carbonation-induced corrosion.
This paper compared the initial surface absorption of conventional concrete and laterized concrete containing Portland cement (PC) and sawdust ash (SDA). Laterized concrete was produced at laterite contents of 15 and 30% as partial replacement for sand and SDA contents of 10 and 20% as partial replacement for PC. Compressive strengths at 28 days and initial surface absorption after 10 minutes (ISA-10) at 28, 60 and 90 days were determined at the water/cement ratios of 0.35, 0.50 and 0.65 and assessed at equal 28-day strengths of 25-35 N/mm2. At equal water/cement ratios, compressive strength reduced and ISA-10 increased with increasing content of laterite and SDA. On the other hand, compressive strength and resistance to surface absorption of the blended cement laterized concretes increased with increasing curing age. At equal strengths, all the blended cement laterized concretes have better resistance to surface absorption than the conventional PC concrete.
Heat of hydration up to 72 hours and compressive strength up to 7 days of Portland cement and 17 binary and ternary cements containing fly ash, silica fume, and metakaolin, at a water/cement ratio of 0.50 and addition contents of 20%, 35%, and 55%, were used to examine the early-age performance of concrete. Results revealed that early-age performance depends on the fineness, heat of hydration, and dilution effect of cement combinations. Fly ash, due to dilution effect, reduces the heat of hydration and compressive strength. Using silica fume and metakaolin with increasing content of up to 10% as binary and ternary cement components, due to their fineness and increased heat of hydration, supports the strength development. Most of the cement combinations met the standard of strength requirements for ordinary early-age performance of concrete, while only half of it satisfied the standard for high early-age performance.
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