Concrete Deterioration Statistical Analysis Case Study

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Table of Contents

Introduction
Literature Review
Statistical Analysis
Discussion of Results
Conclusion
Reference List

Introduction

Background

Concrete is a conventional building material because it is not only durable but also made easily during construction. Concrete deterioration is one of the major issues in the construction industry that causes defects in structures. The understanding of the causes and the rate of concrete deterioration forms the basis of constructing enduring structures. Normally, concrete deterioration is subject to numerous forces, which collectively contribute to overall deterioration. Poor construction practices, harsh weather conditions, and chemical reactions are some of the major causes of concrete defects in most structures. According to Gollu et al. (2016), aggregate expansion, bacterial corrosion, seawater effects, chemical damage, calcium leaching, and physical damage are some of the causes of concrete defects. In essence, physical, chemical, and biological factors interact in the environment and contribute to the deterioration of concretes.

The nature of defect varies depending on the causes and exposure condition resulting in the formation of the hairline crack, single crack, multiple cracks, minor spalling, severe spalling, spalling on exposed reinforcement, demolishing, minor repair, or major repair. The defects also varied according to the construction designs such as in-situ reinforced, composite in-situ, composite, pre-stressed, precast, plain, culvert, brick, box culvert, and barrel rail parapet types of concretes. Structures can be footbridges, over-bridge, under-bridge, gantry bride, or wall. When defects occur, they can fall under insignificant, serviceable, or very significant in the aspect of urgency repair. In this view, this research paper examines member type, exposure condition, and urgency of repair relative to three types of concrete defects, namely, minor defects, minor spalling, and major deterioration.

Problem Statement

Concrete deterioration is a major issue in the construction industry because it reduces the durability of structures, weakens the stability of buildings, causes the loss of lives, and contributes to the loss of property. Since there are numerous causes of concrete deterioration, which range from structural design to environmental factors, it is difficult to point out the exact cause of a specific deterioration (Gollu et al. 2016). Some concrete effects occur due to a single cause while others occur due to multiple causes. To understand the causes of concrete defects, construction engineers need to identify real causes and recommend appropriate repair interventions to prevent the occurrence of major structural disasters. Nepal and Chen (2015) explain that reinforcement corrosion is a major problem in the construction industry because it contributes to the occurrence of concrete defects and structural disasters. The adequate inspection of structures for concrete defects requires the understanding of diverse causes and the degree of their impacts on different forms of concrete deteriorations. In this view, a comparison of the degree of defects with exposure condition, the urgency of repair, and member type of defect would provide important information about the causes and the occurrence of concrete defects.

Aims and Objectives

To determine the relationship between member type of defect and the defect number of concrete defects that occurred on the bridge.
To determine the relationship between the exposure condition and the defect number of concrete that occurred on the bridge.
To establish the relationship between the urgency of repair and the defect number of concrete occurred on the bridge.

Literature Review

Across the globe, there is an increasing concern for premature deterioration of concrete structures. Narwaria and Tiwari (2016) note that minor concrete defects hasten the deterioration of concretes for they allow leakage and passage of water, chemicals, oxygen, and other gases. Essentially, the lack of standardization in the design of concretes is one of the factors that contribute to premature deterioration of structures. In this view, Narwaria and Tiwari (2016) recommend the expansion of standard and effective alignment with exposure conditions provides an effective way of predicting deterioration and sustainability of structures. Therefore, effective classification of exposures and defects enables prediction of deterioration of concrete structures and optimize maintenance operations.

Visual inspection of concrete defects is necessary to detect minor defects and prevent their progression into minor spalling and major deterioration. Given that diverse causes contributes to the occurrence of concrete defects, construction engineers hold that the common preventable causes are inferior workmanship, corrosion of steel, poor design of structures, and inadequate specifications of concrete components. Corrosion of steel used in reinforcing steel is a serious cause of concrete defect because it results in structural collapse, loss of property, and even lives (Gollu et al. 2016). Moisture, temperature, chemical factors, physical factors, and biological factors contribute to corrosion of reinforcing steel and concrete defects. According to Estokov et al. (2012), Acidithiobacilli spp is bacteria that oxidize sulfur and corrode concretes resulting in their deterioration. Excess moisture and high temperature causes expansion of concrete and destabilizes cement resulting in concrete defects such as cracks, spalling, and major deterioration.

Chemicals such as salt and sulfuric acid hasten corrosion while physical factors such as abrasion, stress, and strain cause concrete defects. In their study, Zhang et al. (2014) established that alkali reactions and freeze-thaw cycles are major causes of spalling and cracks. As biological factors, plants, fungus, sponges, and bacteria cause concrete defects by releasing chemicals that speed up the corrosion of steel and deterioration of concrete. Thus, understanding of the extent and degree to which these factors contribute to concrete defects is critical in the protection of concrete, prevention of deterioration, and enhancement of durability.

Construction engineers have classified concrete defects according to member type, exposure condition, possible cause, defect, construction design, structure type, and the urgency of repair. The classification of concrete defects is important for it allows construction engineers to assess the degree and the nature of defects so that they can make appropriate repairs and strengthen structures (Gollu et al. 2016). Member type is a form of concrete defect that measures strengths of concrete in terms of flexural, compression, joint, parapet, and other forms of strength. As the degree of exposure determines the rate of deterioration, the exposure condition can be mild, moderate, severe, very severe, or extreme. The possible causes of concrete defects can be early age cracking, over-stressing, impact, corrosion, or a combination of unknown causes.

Regular inspection of buildings is essential for effective maintenance and prevention of disasters. As outdoor climatic conditions cause concrete deterioration, construction engineers assume that they deteriorate faster and require urgent repair than unexposed parts. In their assessment of deterioration of concrete in outdoor conditions, Lahdensivu et al. (2013) found out that lack of systematic assessment results in inexpensive maintenance of structures due to early and unnecessary repairs. In this view, construction engineers should assess structures and take precautions not to overlook damages or undertake unnecessary repairs while concrete is still strong.

Statistical Analysis

Histograms

Minor Defects

The histogram below (Figure 1) shows that the exposure conditions that cause minor defects (defect number 3) are mild, moderate, and severe exposures.

Shows that the urgency of repair for minor defects are mostly insignificant, serviceable, and rarely very significant. — *Figure 2 shows that the urgency of repair for minor defects are mostly insignificant, serviceable, and rarely very significant.*

*Figure 3: Regarding member type, Figure 3 indicates that most of the defects are flexural and compression while few are parapet and others.*

Minor Spalling

*Figure 6: In the aspect of member type, Figure 6 shows that most minor defects are flexural and compression followed by parapet and others.*

Major Deterioration

*Figure 9: Regarding the member type, most of the deteriorations are flexural and compression while some defects are joined, parapet, and others.*

Descriptive Statistics

Descriptive Statistics for Minor Defects

Table 1

Descriptive Statistics
		The exposure for bridge defect 3	The urgency of repair status of bridge defect 3	Member type3
N	Valid	51	55	55
N	Missing	4	0	0
Mean		1.63	1.60	2.07
Median		2.00	2.00	2.00
Std. Deviation		.631	.627	1.399
Variance		.398	.393	1.958
Range		2	2	4
Interquartile range		1	1	1
Quartiles	25	1.00	1.00	1.00
	50	2.00	2.00	2.00
	75	2.00	2.00	2.00

Descriptive Statistics for Minor Spalling

Table 2

Descriptive Statistics
		The exposure for bridge defect 7	The urgency of repair status of bridge defect 7	Member type7
N	Valid	245	247	246
N	Missing	2	0	1
Mean		1.67	1.90	2.43
Median		2.00	2.00	2.00
Std. Deviation		.647	.624	1.531
Variance		.419	.389	2.344
Range		2	2	4
Interquartile range		1	0	1
Percentiles	25	1.00	2.00	1.00
	50	2.00	2.00	2.00
	75	2.00	2.00	4.00

Descriptive Statistics for Major Deterioration

Table 3

Descriptive Statistics
		The exposure for bridge defect 9	The urgency of repair status of bridge defect 9	Member type9
N	Valid	92	92	92
N	Missing	0	0	0
Mean		1.67	2.50	2.07
Median		2.00	3.00	1.00
Std. Deviation		.648	.602	1.397
Variance		.420	.363	1.952
Range		2	2	4
Interquartile range		1	1	2
Quartiles	25	1.00	2.00	1.00
	50	2.00	3.00	1.00
	75	2.00	3.00	2.75

Probability Distribution Plot

P-P Plot for Minor Defects

*Figure 12: Normal P-P Plot of Member Type3*

P-P Plot for Minor Spalling

*Figure 14: Normal P -P Plot of the Urgency of Repair Status of Bridge Defect7*

*Figure 15: Normal P -P Plot of Member Type7*

P-P Plot for Major Deterioration

*Figure 17: Normal P -P Plot of the Urgency of Repair Status of Bridge Defect9*

*Figure 18: Normal P -P Plot of Member type 9*