Enhancing Concrete Early Strength

concrete early strength is the peak of concrete compressive strength obtained at a short period of time after its placement. Normally, strength evaluations are carried out at the standard age of 7 and 28 days after the concrete is placed. This short period of time is important for the construction industry because it allows rapid form reuse, fast production of precast concrete elements and quick repair of pavements in order to reduce traffic downtime.

Often the high early strength of concrete is achieved by using an accelerating chemical admixture, which accelerates the rate of hydration and consequently the concrete early strength development. However, the use of this type of admixture increases the risk of corrosion of steel reinforcement and can have other adverse effects on the concrete properties.

In this paper, an alternative method of enhancing concrete early strength is proposed by using Sporosarcina pasteurii bacteria as an admixture. This admixture enhances the early strength of concrete by increasing the formation of secondary cementitious compounds and therefore improving the concrete hydration. Unlike the commonly used sodium carbonate or urea, this admixture has no detrimental effect on the concrete rheology and initial setting time.

A combination of ordinary Portland cement (OPC) with a calcium sulfoaluminate (CSA) binder and Na2SO4 as an accelerator was tested. This CSA-based binder showed good performance and it was possible to achieve a concrete compressive strength of >5 MPa/12 h through its activation of initial hydration at low temperature curing.