Introduction

One of the oldest and most commonly used construction materials in the world is concrete. This is major because it is readily available, less expensive, durable, strong, and can withstand extreme weather conditions (Li, 2011). Concrete is a heterogeneous mixture that consists of fine aggregate (sand), coarse aggregate (granite), a binding medium (cement), water, and in some cases admixtures (accelerators, retarders, and superplasticizers) (Tantawi, 2015). Concrete is vital in the construction of several infrastructures all over the world ranging from; residential buildings, industrial structures, roads, highways, bridges, parking structures, concrete sleepers, etc. (Neville, 2006).

Materials scientists, engineers, chemists, and construction professionals have aided the concrete industry in improving workability, environment, ability to monitor working hours, durability as well as strength of Portland cement concrete by integrating some additional substances regarded as admixtures. The function of each admixture on concrete aims at a specific need (Jayaraman et al., 2016). According to Shah, Shah, and Pitroda, (2014), chemical admixtures are chemicals applied before or during the process of concrete mixing before the placing of concrete, for the purpose of changing and modifying certain properties in fresh and hardened concrete. Admixtures or additives used in concrete are plasticizers, retarders, and accelerators (Tantawi, 2015).

Accelerators or accelerating admixtures are water-soluble inorganic chemicals added to a concrete mix to increase the reaction between water and cement (cement hydration reaction) thus accelerating the setting (i.e., reducing setting time) and the early strength development of concrete (Al-neshawy, 2020; Fahl, 2009). They also reduce the time used for proper curing. Some accelerators only affect either setting or hardening, while others accelerate both setting and hardening (Dodson, 1990). Accelerators are classified as Type C admixtures under ASTM-C 494 (AASHTO M 194). Accelerators are mainly used in cold weather because concrete setting time is usually delayed. Calcium Chloride (CaCl₂) is the most commonly used accelerator admixture (Yurdakul, Jackson, and Rieder, 2017).

Retarders, set retarders, or retarding admixtures are added to concrete to delay the concrete setting time (Tantawi, 2015). According to Lea, (1988) retarders (sugar) when in contact with water causes a cement particle to pass out a stream of calcium ions into the ambient water and any substance able to stop or delay this surge will also retard the reaction between the water and the cement particle, thereby slowing down the process of hydration. They are used in hot weather, or in cases when concrete has to be conveyed to a construction site distant from the production site.  Additionally, set retarders also improve the workability of concrete. They are classified as Type B, D, and G under ASTM-C 494 (AASHTO M 194). The most commonly used retarders are sugar and gypsum.

Super-plasticizers are used to improve the workability of concrete while reducing the amount of water used for mixing concrete, since the strength of concrete increases when the water-cement ratio decreases (Tantawi, 2015; Houst et al., 2008). They are referred to as high-range water-reducing admixtures because of their ability to reduce three to four times the water required for mixing in a specific concrete mixture as opposed to normal water-reducing admixtures (Dransfield, 2003). The addition of superplasticizers to mortar or concrete reduces the water-cement ratio without negatively impacting the workability of the paste. They greatly improve the performance of the hardening fresh paste. Additionally, they are used to produce high-strength concrete. They are classified as Types F (water-reducing) and Type G (water reducing and retarding) under ASTM C-494 (AASHTO M 194).

Problem Statement

Admixtures in concrete are very important and their function cannot be over-emphasized as they help solve many problems associated with ordinary concrete (Shah, Shah, and Pitroda, 2014). Presently, there is a need for speed and flexibility in the usage of concrete in the construction industry, hence the need for admixtures to help deal with these constraints. Concrete in cold weather takes a longer time than usual for curing and setting to take place. Conversely, in hot weather concrete sets and hardens faster than normal. Also, during summer (dry season), when there is a need to hasten the set time and curing process of concrete to make concrete set faster and to promote the early strength development, accelerators are of great importance. Retarders play a major role in helping concrete slowly set and harden in extremely hot weather cases. Also, in cases when the production of concrete with high workability for easy placement is needed as well as in the production of high strength concrete with normal workability but lower water content, super-plasticizers are effective (Shah, Shah, and Pitroda, 2014).  Furthermore, admixtures are normally added in ratios not more than 2% of cement content, because an increase in its addition decreases concrete strength (Tantawi, 2015), therefore the need to evaluate these admixtures available in several quarters globally to determine their optimum dosages for different concrete mixes.

Aim and Objectives

The aim of this research is to determine the effect of admixtures (set-retarder, accelerator, and superplasticizer) on the workability, setting times, and compressive strength of concrete mixes.

The objectives of the research work are;

• Objective 1: To carry out tests on the physical property of cement and aggregates.
• Objective 2: To evaluate the change in workability, setting times (initial and final), and compressive strength of concrete for the variableness in dosages of admixtures (set-retarder, accelerator, and superplasticizer) which helps in measuring the dosage of admixtures to be used in a fresh concrete mix.
• Objective 3: To determine the workability, setting times, and compressive strength of several samples.
• Objective 4: To juxtapose the experimental results from the application of these admixtures (separately and together) with standard regulations.

Research Questions

The identified research questions for this project are provided below:

• What are the properties of concrete without applying these admixtures?
• What is the need for applying these admixtures?
• What is the method of application of these admixtures to concrete?
• How do they influence the workability of concrete?
• How do they influence the initial and final setting times of concrete?
• How do they influence the compressive strength of concrete?

Deliverables

The deliverables of this project are a project report, samples of the concrete with applied admixtures, and gotten results. the samples would be tested according to ASTM (American Society for Testing and Materials) standard and literature to see how they compare with required standards. Cubes, cylinders, and beams would be cast to test concrete samples. Also, the report should contain complete documentation of the laboratory experiment procedure from start to finish, how various process variables and results were gotten, the methods adopted for the tests, as well as the period of time and instruments/equipment used for the tests and study.

Relevance

This project focuses on investigating the effect of using admixtures such as set-retarder, accelerator, and superplasticizer on the workability, setting times, and compressive strength of concrete mixes, in order to provide a better, stronger, more workable, and durable concrete for construction.

Methodology

This project focuses on secondary research, laboratory experiments, and process analysis. They are discussed below:

Secondary Research

The secondary research in this project will utilize a systematic approach (Johnson et al., 2016) to review the works of literature. The steps involved in the systematic review of the literature are provided below:

• Step 1: Identify the research questions that can be used for the project.
• Step 2: Identify the keywords that should be used to research the works of literature.
• Step 3: Extract the journals and books that are appropriate for this project.
• Step 4: Write the literature review chapter.

Laboratory Experiments

The laboratory experiments would cover a large part of this project. They would be carried out in stages, and as such described below;

• Stage 1: Purchasing the admixtures (set-retarder, accelerator, and superplasticizer) from the market.
• Stage 2: Collection of aggregates (fine and coarse), cement, potable water, and other constituents of concrete.
• Stage 3: Preparation of laboratory, equipment, and instruments to be used for the test.
• Stage 4: Developing an appropriate process route and optimal equipment arrangement for an efficient process setup for the tests.
• Stage 5: Application of admixtures and casting of concrete on several varied admixture dosages and concrete mixes.
• Stage 6: Carrying out workability, setting times, and compressive strength tests on samples.
• Stage 7: Result testing, analysis, and evaluation.

Process Analysis

The totality of the process reaction would be analyzed and this would also occur in stages;

• Stage 1: Process Testing
• Stage 2: Process Control
• Stage 3: Process Optimization

Evaluation

The risk assessment conducted for this project is provided in the table below:

Table 1:  Risk assessment

Schedule

Table 2: Project Plan

References

Al-neshawy. (2020). Lecture 3 . Concrete Admixtures. 1–24.

Dodson. (1990). Concrete Admixtures.

Dransfield. (2003). Admixtures for concrete, mortar, and grout. In Advanced Concrete Technology. Woodhead Publishing Limited. https://doi.org/10.1016/B978-075065686-3/50280-9

Fahl T. P., 2009. Concrete Principles, 2nd ed., American Technical Publishers, Inc.

Houst, Y. F., Bowen, P., Borget, P., & Galmiche, L. (2008). Design and Function of Novel Superplasticizers for More Durable High-Performance Concrete ( Superplast Project ). October. https://doi.org/10.1016/j.cemconres.2008.04.007

Jayaraman Anitha, Pradeepa S, Soni Lalit., and Rakshit K.B (2016). Influence of Admixtures on Behavior of Concrete. International Journal of Research in Advent Technology, 4(11). www.ijrat.org

Johnson, D., Deterding, S., Kuhn, K.A., Staneva, A., Stoyanov, S., and Hides, L., 2016. Gamification for health and wellbeing: A systematic review of the literature. Internet interventions, 6, pp.89-106.

Lea, F.M. 1988. The chemistry of cement and concrete. 3rd ed., Edward Arnold, London, UK.

Li Z., 2011. Advanced Concrete Technology, John Wiley & Sons, Inc.

Neville, A.M. 2006. Properties of concrete. 4th ed., Dorling Kindersley, New Delhi, India.

Shah Darshan, Shah Meet and Pitroda Jayeshkumar (Prof.) 2014. CHEMICAL ADMIXTURES: A MAJOR ROLE IN MODERN CONCRETE MATERIALS AND TECHNOLOGIES. National Conference on: “Trends and Challenges of Civil Engineering in Today’s Transforming World”, Civil Engineering Department S.N.P.I.T. & R.C., Umrakh.

Tantawi, H., 2015. Introduction to Concrete Technology. Department of Civil Engineering, Fahad Bin Sultan University.

Yurdakul, E., Jackson, N., & Rieder, K.-A. (2017). Role of chemical admixtures in improving wet-mix shotcrete performance for ground support. Proceedings of the Eighth International Conference on Deep and High-Stress Mining, January 2017, 723–731. https://doi.org/10.36487/acg_rep/1704_49_jackson

Last updated: Jan 10, 2022 04:24 PM