**1.1. General**

It is well known that a lot of ground granulated blast furnace slag (ggbfs) is produced in the steel-iron industry every year throughout the world. By utilizing this by-product it would help reduce the environmental problems and also provide significant economic benefits. The results of several researches have also shown that the use of replacement materials in mortars and concretes improves durability, which is crucial for structures built in aggressive environments, e.g. in marine structures and structures such as large tunnels and bridges with long life spans. For every ton of Portland cement manufactured, approximately one ton of CO2, in addition to greenhouse gases, is released into the atmosphere. Therefore, if the part of the Portland cement can be replaced by waste materials, e.g., slag, then the amount of cement needed and hence, the amount of CO2 released into the atmosphere can be reduced (Lodeiro, Macphee, et al., 2009). Consequently, ggbfs is being widely used as a cement replacement in Portland cement mortar and concrete for improving mechanical and durability properties.

The use of ggbfs has certain advantages because of its excellent cementitious properties over OPC and it is sometimes used due to the technological, economic and environmental benefits. However, the use of slag has been limited because of the disadvantage of its low early strength (Bougara, Lynsdale, et al., 2009). The major factors affecting the early age strength development of mortars and concrete are as follows:


Concretes made with ggbfs have many advantages including improved durability, workability and economic benefits.

Mortar is a workable paste used to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, cinder blocks, etc. Modern mortars are typically made from a mixture of sand, a binder such as cement or lime, and water. Based on (ACI, 2006) there are four different types of mortars commonly used in building projects namely Type N, Type M, Type S, and Type O. Type N mortar is a medium strength mortar, which means that it is suitable for use both on indoor projects and on outdoor projects that are above grade. Type M mortar is a high strength mortar. Due to the strength of Type M it is usually used in heavy load bearing walls, although it is also sometimes used in other heavy duty applications like masonry that is below grade or that comes in contact with the earth such as retaining walls or foundations. Type S mortar is also a relatively high strength mortar which is suitable for below grade projects and heavier outdoor projects. Type O mortar is the lowest strength mortar and is suitable only for indoor, lightweight applications. The most commonly used mortars for most home improvement projects are Type N and Type S. Type N is chosen for lighter weight or indoor projects, and Type S for projects that require a heavier duty mortar. All of the different types of mortar are made with the same ingredients. The only difference is the proportions of each ingredient in the mix whether for availability considerations or for minimizing the number of different mortar types on the job site. The OPC-slag mortars can be classified into three groups as OPC mortars (OMs), slag mortars (SMs), and OPC-slag mortars (OSMs).

Using "Heat Treatment" Method for Activation of OPC-Slag Mortars 387

Different amounts of slag as replacement for cement were used and the optimum level of replacement was determined. In this investigation only one source of slag was used and the optimum level of replacement was used throughout the study. The optimum level was

The focus of this project is to activate OPC-slag mortars using heat treatment (thermal activation method). In this activation method different temperatures within the range of 40 °C to 90 °C were used for activation. The mortars were heated for duration of 2 to 26 hours. The mechanical properties studied in this research are compressive strength at the both early and later ages, strength loss and strength development at later ages of OPC-slag mortars in duration of up to 90 days. The compressive strengths throughout the study were

Before discussing the activation method, the determination of the optimum level of

This section reports on the testing of fourteen OPC-slag mortars (OSMs) and two control OPC mortars (OMs) and slag mortars (SMs). The main aim is to determine the level of cement replacement with slag to achieve higher early strength with reasonable flow. The variable is the level of ggbfs in the binder. Graded silica sand was used in all mixes. It was determined that the optimum level of replacement slag is within the range of 40% to 50% of OPC (Ahmed, Ohama, et al., 1999). The optimum level is defined as the replacement level of slag with the highest compressive strength, when used in the mortar while strength loss is

It is intended to find the optimum cement at replacement level with slag that gives the highest early strength at 7 days and especially 3 days without the use of any activation method. From Figure 1 it is clear that whenever the level of replacement is more than 40% the early strength at 3 days will be reduced. It can also be seen that although for replacement levels 10%, 20%, and 30% the early strength at 3 days is approximately the same, but, generally with an increase in the slag level from 10% to 40% the early strength increases. However, the early strength at the 40% level is the highest, i.e. 42.4 MPa. Based on the results obtained it can be seen that by increasing the replacement level to more than 40%, the early strengths decreased significantly. This shows that the optimum level of replacement is 40% at 3 days. The same variations for 7-day strengths were observed albeit with slight changes. At 40% optimum level of replacement slag, the strength at 7 days is 55.8

based on high early strength and lowest strength loss for the mortar mixes.

tested for the specimens at 1, 3, 7, 28, 56, and 90 days.

replacement of slag in OPC-slag mortars is discussed.

**2. Determination of optimum level** 

**2.1. Introduction** 

the lowest.

**2.2. Replacement level** 

*2.2.1. Optimum replacement level* 

## **1.2. Research significance**

Based on the related literature review there is not much research work regarding activation of OPC-slag mortars, and this is the main purpose of this investigation. In this study, the thermal activation method was used. The compressive strength loss was studied in this research at early and later ages. Strength development of OPC-slag mortars without and with use of activation method was also studied for duration up to 90 days and some regression relationships was suggested. Using the suggested relationships a criterion to forecast the strength behavior of OPC-slag mortars at later ages is established.

## **1.3. Research objectives**

The objectives of this research are as follows:


## **1.4. Scope of work**

The objective of this study is to use higher percentage of replacement slag as possible without any reduction in mechanical properties of mortar such as compressive strength. Different amounts of slag as replacement for cement were used and the optimum level of replacement was determined. In this investigation only one source of slag was used and the optimum level of replacement was used throughout the study. The optimum level was based on high early strength and lowest strength loss for the mortar mixes.

The focus of this project is to activate OPC-slag mortars using heat treatment (thermal activation method). In this activation method different temperatures within the range of 40 °C to 90 °C were used for activation. The mortars were heated for duration of 2 to 26 hours. The mechanical properties studied in this research are compressive strength at the both early and later ages, strength loss and strength development at later ages of OPC-slag mortars in duration of up to 90 days. The compressive strengths throughout the study were tested for the specimens at 1, 3, 7, 28, 56, and 90 days.
