Fairly and Rapidly Assessing Low Carbon Concrete Made with Slowly Reacting Cements

TY - GEN

T1 - Fairly and Rapidly Assessing Low Carbon Concrete Made with Slowly Reacting Cements

AU - Jozwik, Maciej

AU - Jones, Rod

AU - Newlands, Moray

AU - MacPhee, Donald

PY - 2023/6/28

Y1 - 2023/6/28

N2 - The CIIIA+SR combination in BS 8500-1 accounts for around 40% of UK ready-mixed concrete production and will normally consist of 50%-55% GGBS. The slower setting times and strength gain, especially at lower ambient temperatures, can cause issues with finishing due to extended bleed and programming due to extended stripping times. Contractors have become accustomed to these challenges, however the performance of the lower clinker cements in EN 197-5 will present an even bigger challenge compared to their binary equivalents. Low carbon alternatives typically require anywhere between 90 and 180 days of standard water curing to reach equivalent standard 28-day concrete maturity. Whilst this has significant implications for programming of construction work, it is also difficult to make material performance comparisons within timescales suitable for clients and designers to make decisions on material specification. A range of cement type combinations were cast using typical w/c ratio used for structural and non structural concrete (0.4, 0.5 and 0.6 w/c). Elevated temperature curing regime (at 50°C) was investigated by means of comparative performance against standard water cured samples. Analysis involved comparison of compressive strength development to establish strength-based equivalent maturity. MIP and SEM were done to investigate both porosity and physical microstructure of test specimens. Compressive strength equivalency was used as a proxy for equivalent degree of maturity of investigated concrete compositions. The research shows that 21-day elevated temperature cured samples are very similar to 90-day standard cured specimens in terms of both compressive strength and internal physical microstructure. The similarities diverge with increasing water-cement ratio with little compressive strength equivalency for concretes cast at 0.6 w/c. However, the microstructure remains similar suggesting equal degree of maturity for both elevated and standard cured samples of corresponding cement type concretes for all investigated water-cement ratios.

AB - The CIIIA+SR combination in BS 8500-1 accounts for around 40% of UK ready-mixed concrete production and will normally consist of 50%-55% GGBS. The slower setting times and strength gain, especially at lower ambient temperatures, can cause issues with finishing due to extended bleed and programming due to extended stripping times. Contractors have become accustomed to these challenges, however the performance of the lower clinker cements in EN 197-5 will present an even bigger challenge compared to their binary equivalents. Low carbon alternatives typically require anywhere between 90 and 180 days of standard water curing to reach equivalent standard 28-day concrete maturity. Whilst this has significant implications for programming of construction work, it is also difficult to make material performance comparisons within timescales suitable for clients and designers to make decisions on material specification. A range of cement type combinations were cast using typical w/c ratio used for structural and non structural concrete (0.4, 0.5 and 0.6 w/c). Elevated temperature curing regime (at 50°C) was investigated by means of comparative performance against standard water cured samples. Analysis involved comparison of compressive strength development to establish strength-based equivalent maturity. MIP and SEM were done to investigate both porosity and physical microstructure of test specimens. Compressive strength equivalency was used as a proxy for equivalent degree of maturity of investigated concrete compositions. The research shows that 21-day elevated temperature cured samples are very similar to 90-day standard cured specimens in terms of both compressive strength and internal physical microstructure. The similarities diverge with increasing water-cement ratio with little compressive strength equivalency for concretes cast at 0.6 w/c. However, the microstructure remains similar suggesting equal degree of maturity for both elevated and standard cured samples of corresponding cement type concretes for all investigated water-cement ratios.

KW - cement

KW - Concrete

UR - https://www.fce.vutbr.cz/stm/fracture/symposium2023/

M3 - Conference contribution

SN - 9788087434093

SP - 107

BT - Non-Traditional Cement & Concrete

A2 - Bilek, Vlastimil

A2 - Khestl, Filip

A2 - Miarka, Petr

A2 - Seitl, Stanislav

T2 - 7th International Conference on Non-Traditional Cement and Concrete

Y2 - 25 June 2023 through 27 June 2023

ER -