Low Carbon Self-healing Concrete—Mixture Analysis

The slow creep of microcrack evolution into structural damage and the high embedded carbon value in high Ordinary Portland Cement (OPC) concrete mixtures are commonly found in reinforced concrete structures and infrastructure. To test the viability and performance of new and greener alternatives to ordinary Portland cement in concrete, these mixtures of fly ash or Pulverised Fly Ash (PFA) and a bacterial self-healing agent are being used to replace cement in concrete partially. OPC has the most embedded carbon values in concrete, making reducing this element a priority. This paper compares the mechanical properties of concrete mixtures with Ground Granulated Blast-furnace Slag (GGBS) and fly ash with an added bacterial self-healing agent that heals microcracks. To allow observation of the evolution of these novel concrete mixtures, a series of mechanical tests are performed throughout the 7, 14, 28 and 90 days of curing. These include the evaluation of compression, flexural, tensile splitting strength and dynamic elastic modulus. There is a reduction in mechanical capacity when added PFA, and even further with the self-healing agent, in the same fashion as using GGBS. Thus to improve the early day's mechanical properties, another fly ash mixture was created with an accelerator and plasticiser to counteract these reductions. A step closer to a carbon-free environment is made with reduced embedded carbon values between 39 and 43% while keeping almost the same properties of a fully OPC-based control mix. A self-healing agent that can seal cracks between 0.3 mm and 0.8 mm in theory but is also seen to seal up to 1.5 mm will allow a decrease in structural maintenance and cost frequency while reducing the embedded carbon value of edified concrete structures. The capacity to be used intrinsically with a fresh concrete mixture and extrinsically to concrete cracked surfaces gives the bacterial self-healing agent a versatile range of applications. These novel mixtures will expand a structure's service life whilst allowing the retrofitting of existing structures.