Effect of Curing Methods on the Compressive Strength of Cement Concrete

Effect of Curing Methods on the Compressive Strength of Cement Concrete
CHAPTER ONE: INTRODUCTION
1.1 Background of the Study
Concrete curing is the process of controlling the rate and extent of moisture loss, relative humidity, and temperature from newly poured concrete for a certain period of time after it has been cast or finished to ensure that the cement has been properly hydrated and the concrete has hardened . The American Concrete Institute (ACI) defines curing as the measures taken to maintain adequate moisture and temperature conditions in freshly placed concrete so that hydration of the cement can continue. The importance of curing cannot be overstated: inadequate or poorly timed curing can lead to premature drying, interrupted hydration, microcracking, and long-term durability failures in concrete infrastructure .
The compressive strength of concrete is the most important mechanical property used in structural design and quality assurance. While the water-cement ratio and the properties of constituent materials determine the potential strength of a concrete mixture, the actual strength achieved depends significantly on the curing regime adopted. Effective curing increases strength, volume stability, durability, abrasion resistance, impermeability, and resistance to freezing and thawing . Conversely, if adequate curing is not performed, the effort required to control the quality of materials and the production of concrete can be discounted .
A variety of curing methods are employed in construction practice, each with distinct mechanisms, advantages, and limitations. The traditional method of ponding or immersion curing involves submerging concrete specimens in water, providing continuous moisture for hydration. Wet covering methods, such as burlap or jute bags, maintain surface moisture through regular wetting. Sprinkling or spraying provides intermittent water application. Membrane-forming curing compounds create a barrier to moisture evaporation. Air curing, which involves no deliberate moisture retention, serves as a control condition but typically produces inferior results.
Experimental research consistently demonstrates that curing method significantly impacts concrete compressive strength. A study conducted in Nigeria using a mix ratio of 1:2:4 and water-cement ratio of 0.5 found that ponding achieved the highest compressive strength and density, followed by wet covering, sprinkling, then uncured for two days, with totally uncured cubes having the least compressive strength and density . Research under Abuja climatic conditions showed that water curing produced the highest 28-day compressive strength of 36.81 N/mm², followed closely by jute bag curing with 34.04 N/mm², banana leaf curing with 31.77 N/mm², and polyethylene foam curing with 27.33 N/mm² . A statistically rigorous study using ANOVA and Cohen's d effect size analysis found that water submersion achieved superior performance (23.55 ± 2.25 MPa) representing large practical significance (Cohen's d = 1.09) compared to ambient curing (21.13 ± 2.09 MPa), while jute covering showed moderate effectiveness and superabsorbent polymer internal curing demonstrated negligible improvement .
In tropical climates such as Nigeria's, where temperatures are high and relative humidity can be low, concrete curing presents particular challenges. Hot dry environments hasten the drying of concrete and are thus far more dangerous than cool damp environments . Rapid moisture loss from fresh concrete can interrupt hydration and cause plastic shrinkage cracking, compromising both strength and durability. Understanding the relative effectiveness of different curing methods under these conditions is therefore of critical importance for construction practice.
1.2 Statement of the Problem
Despite the well-established importance of curing, field practice often falls short of recommended standards. In many construction projects, curing is treated as a low-priority activity that is easily sacrificed when schedules are tight or resources are constrained. Curing durations are frequently shortened, and the selection of curing methods is often based on convenience rather than on systematic evaluation of performance.
The Nigerian construction industry faces specific challenges related to curing. High ambient temperatures accelerate moisture evaporation, making adequate moisture retention more difficult. Water scarcity in some regions limits the feasibility of traditional ponding or sprinkling methods. Inadequate site supervision can result in curing being neglected altogether. Furthermore, while numerous studies have investigated curing methods, the results vary depending on materials, mix proportions, curing parameters, and environmental conditions, making it difficult to generalize findings across different contexts.
There exists a need for systematic, controlled experimental investigation of curing methods specifically applicable to Nigerian conditions, using locally available materials and commonly adopted mix designs. Such investigation should compare not only traditional water-based methods but also alternative methods that may be more practical under local constraints, including wet covering with locally available materials and membrane-forming curing compounds.
1.3 Aim and Objectives
The aim of this study is to investigate the effect of different curing methods on the compressive strength of cement concrete, with a view to identifying the most effective methods for use under Nigerian climatic conditions.
The specific objectives are:
1. To determine and compare the compressive strength of concrete cured by different methods—water immersion (ponding), wet burlap covering, sprinkling, curing compound application, and air curing—at curing ages of 7, 14, and 28 days.
2. To evaluate the influence of curing method on the rate of strength development.
3. To assess the density and water absorption characteristics of concrete cured by each method.
4. To identify the most effective curing method in terms of compressive strength achievement and practicality under Nigerian conditions.
1.4 Scope of the Study
This investigation focuses on normal-strength concrete produced with Ordinary Portland Cement (OPC), river sand as fine aggregate, and crushed granite as coarse aggregate. A nominal mix of 1:2:4 (cement:sand:coarse aggregate) with a water-cement ratio of 0.5 is adopted, consistent with common practice for normal concrete in Nigeria. Five curing methods are investigated: immersion in water (ponding), wet burlap covering, sprinkling, curing compound application, and air curing (control). Compressive strength is evaluated at 7, 14, and 28 days. The study is limited to laboratory conditions and does not include field trials or long-term durability testing beyond 28 days.
1.5 Significance of the Study
The findings of this investigation will provide valuable guidance for construction practice in Nigeria and similar tropical environments. Specifically, the results will:
• Inform curing method selection: Provide comparative performance data to enable engineers and contractors to select curing methods based on strength achievement and site constraints.
• Demonstrate the consequences of inadequate curing: Quantify the strength loss associated with air curing, providing evidence for enforcing curing requirements.
• Evaluate alternative methods: Assess the effectiveness of wet covering and curing compounds as alternatives where water availability is limited.
• Support quality control: Offer benchmark data for verifying curing adequacy against design strength requirements.
• Contribute to research: Establish a reference dataset for future studies on curing optimization and concrete durability in Nigeria.
1.6 Organisation of the Project
This project is organised into five chapters. Chapter One introduces the background, problem statement, objectives, scope, and significance of the study. Chapter Two reviews existing literature on curing theory, the mechanisms by which curing influences strength, and previous experimental studies on curing methods. Chapter Three describes the materials and experimental methods. Chapter Four presents and discusses the results. Chapter Five concludes the study and offers recommendations for practice and future research.
CHAPTER TWO: LITERATURE REVIEW
2.1 Introduction
This chapter reviews the literature on concrete curing and its effect on compressive strength. It begins with the theoretical basis of curing—the role of moisture in cement hydration and strength development—followed by an examination of different curing methods and their mechanisms. The chapter then reviews previous experimental studies, with particular attention to studies conducted under tropical and Nigerian conditions, and identifies gaps in the existing knowledge.