Service life prediction of rc structures made of slag and brick aggregate exposed to saline environment

Abstract

Induction furnace slag (slag) which is an industrial by-product of steel making industry is, of late, produced in large amounts in Bangladesh as well as all over the world. Slag has been used for many purposes in the construction industry, landfilling and agriculture etc. It has a potential for use as aggregate in concrete making. On the other hand, use of brick aggregate is also very common due to easy availability and lower cost. The mineralogical composition of slag may allow its use as an alternate source ofaggregate for particular applications where moderate strength is required. Besides, the environmentally friendly disposal of the large volume of slag is also a matter of great concern. If slag can be used as an alternative aggregate or particularly as an alternative to brick aggregate, it will greatly benefit the society and environment and eventually help to achieve environmentally friendly sustainable development. With the development of the socio-economic conditions of Bangladesh, the construction industry is having rapid growth in the coastal regions, where construction of durable structure is a challenge. In this thesis, experimental investigations have been conducted to evaluate and compare the performance of slag and brick aggregates exposed to the saline environment and predict the service life of structures made of various concrete mixes. The engineering properties, mechanical properties and durability parameters against chloride ingress have been evaluated. A comparison has been made among various durability tests along with establishing a correlation among them. Tests on both concrete cylinder and cube specimens have been made to evaluate and compare various engineering, mechanical and durability properties of concrete made for both types of aggregate. From the experimental results, it can be seen that concrete made of slag provides superior performance in terms of strength and other mechanical properties comparable to concrete made of brick aggregate. It is also shown that concrete made with slag aggregate demonstrates better durability performance in the case of chloride ion ingress and other durability tests. Moreover, slag fulfills the basic requirements mentioned in various codes for an aggregate to be used in concrete other than wearing surfaces. The service life of structures has been predicted as the summation of corrosion initiation time, the time required to initiate the crack and the time for the crack to propagate up to the limit state. As a measure of durability, the service life of structures with different mixes follow a similar pattern for the same environmental exposure for particular parameters and vary with the change of the concrete cover and rebar diameter size. Based on these observed patterns, it has been found that the use of the concrete mixes used in this study for structures exposed to airborne chloride would result in a satisfactory service life of 40 to 60 years as against 30 to 40 years for concrete made using brick aggregate.In severe environment like for the structures subjected to cyclic wet and dry sessions and submerged in seawater, the concrete mixes used in the study have been found to have poor durability. The study has found that the concrete made of slag showed a better performance from durability aspect for all the environmental exposure conditions and slag is suitable for use as aggregate in concrete that requires moderate strength up to 24 MPa. However, there are issues related to handling and workability of concrete made from slag, which would require special care.