Evaluation of the Performance of GGBS Concrete used in Civil and Geotechnical Works

The use of supplementary cementitious materials (SCM) such as Pulverised Fly Ash (PFA) and Ground Granulated Blastfurnace Slag (GGBS) has been proven effective in reducing the total carbon emission of the concrete production process by lowering the use of Ordinary Portland Cement (OPC). The general specifications published by the Government of the Hong Kong Special Administrative Region have allowed the use of PFA as SCM in concrete production for public work projects in the past three decades. From 2012 onwards, the use of GGBS as SCM has also been permitted. In recent years, the local electricity companies have been reducing their reliance on coal-fired plants for electricity generation. The local supply of PFA has been declining and is expected to deplete by the 2030s. Through the management of the concrete mix ID database, the Public Works Central Laboratory (PWCL) noted the trend of using GGBS concrete in public works contracts has been on the rise in the past two years. The PWCL has recently conducted an in-house technical study on the performance of GGBS concrete mixes recently adopted in public works contracts. Based on the original concrete mix formulas and sources of materials, fresh concrete batches were made in laboratory environment. Furthermore, additional concrete test cubes were obtained from available on-going public works construction sites adopting GGBS concrete. Various performance aspects of the concrete mixes, such as the early strength development and shrinkage properties were evaluated. PWCL has also obtained the results of the recent “Low Carbon Concrete Trophy Competition 2022” initiated by the Standing Committee on Concrete Technology and organised by HKIE for comparison purposes. In view of the improved quality of GGBS available in the market in the past few years, PWCL is also planning to conduct a further study on the performance of GGBS concrete, focusing on the recent technological advancement in this area, and the feasibility of achieving higher replacement levels, higher grade strengths with the use of locally available raw materials. This paper summarises our current work on evaluation of the performance of GGBS concrete used in recent public works contracts with the aim of facilitating the industry’s consideration for wider adoption of GGBS concrete in civil and geotechnical engineering works.