Sunday, January 26, 2020
Causes of Concrete Failure
Causes of Concrete Failure Concrete and steel are materials commonly used in building construction. Concrete is formed by mixture of aggregates which are sand and stone, and bonded together by water and cement with the proper ratio of 1:2:4 or 1:3:6 which is commonly used. Steel is a material that is manufactured under carefully controlled condition by which its properties are determined in a laboratory. Combining concrete and steel gives increased strength to resist heavy loads to increase the lifetime of the structure. Even though concrete and steel give many advantages on building, they can also cause failure to the structure thru the impropriate procedure work, and lacks of efficient control and monitoring mechanism (A.M. Neville, 2002),which happen to the concrete column at the building of University of Technology Mara (Ismail M, 2005). The list of previous dissertation topics by building surveying students shows that there has never been a study or research done on concrete failure in the Industrial Zone. Due to the importance of awareness and understanding of concrete failure, the dissertation topic on The Causes Effects of Concrete Failure on Residential Building Surrounding Industrial Zone is chosen for research and case study. The idea on this topic also came when conducting condition survey on the Shah Alam Commercial building where it is important to understand the effects of the emissions produced from industrial area to the concrete structures in order to prevent concrete failure. The aim of dissertation is to give an insight on the causes of the defects, share what measures are taken by the building authority to prevent it and to find the result on the majority causes of the failure and its effect in real case study. The objectives of dissertations are: To study the causes and effects of concrete failure to the building structure To investigate and study the causes and effects of concrete failure of the real life cases i.e buildings in the industrial areas To come up with recommendations to prevent or minimise the concrete failure The scopes of the dissertation are: Literature review on concrete, type of cement and causes of the concrete failure. Case study on the affected residential buildings surrounding industrial zone at section 25 Shah Alam, Klang Valley, and Petaling Jaya. Produce questionnaire and conduct interviews with the contractors, clients, consultant or building maintenance personnel. Analysis of the results based on site observations, reports and interviews To give recommendations based on the result to prevent or minimise the concrete failure on structure. Below shows the procedures to reach the goal for my dissertation. RESEARCH METHODOLOGY CASE STUDY FINDINGS ANALYSIS RESULT (Goal) RECOMMENDATION The dissertation consists of 6 chapters. The dissertation starts with the introduction of the project which includes scopes, objective, and the aims of the project which are stated as chapter 1. Chapter 2 is a literature review on concrete. This includes description on the history of concrete and cement, different types of cement, sources and causes of concrete failure and the main theories of the concrete failure. Chapter 3 discusses the analysis and results of the interviews and questionnaires on concrete failure. The experiences of the relevant people interviewed will be shared in this chapter. Chapter 4 gives the detailed report of the case study including the site condition surveying results which consists of the study of building condition. The investigation and site observation on the causes and sources of defects and the remedies will be discussed. The analysis of the findings and the results of the case study will be captured in chapter 5 which include graphs and discussions. Based on the results, the effectiveness of the remedies will be evaluated in this chapter. The last chapter will conclude the case study and gives recommendations which includes the procedures on preparation and designing a building. Literature Review Introduction There are several impact which carried to the failure of the building. Basicly, failure to the structure such as piling, foundation, ground soil and etc which end up to the disaster or collapsion to the building where blamed appointed to the engineer in-charge and question that unable to explained. In the end, discussion for solving the problem is issue which has proven to the collapsion of Pulbic Work Department at Petaling Jaya (Star Biz, 2009). Therefore, the problems to the concrete which causes by human error during development procedure can be classified as four (4) categories as follow(Zarina Isnin, 2010) :- Design deficiencies Construction error Material defect Maintenance deficiencies However, the purposed of the study is only concerned on the causes and effects to the concrete failures without any concerning specific on the structure ability. Literature review on this chapter which started with the description on the history of concrete and cement and follow by the classification of cement. The objectives of this chapter is to explained the behaviour of the concrete such as sources of failures and its effects based on the facts of previous study and research. History of Concrete and Cement. In around 2,500 BC, Pyramids was the first recorded structure to used cement. The ancient Egyptian constructed Pyramid by mixing mud with straw to bind dried bricks and by adding gypsum cement and lime.Then, the Greek and the Roman found that by adding lime and water, sand and crushed stone or brick and broken tiles, its produce compressional strength and created the first structural material known as concrete. The Pantheon in Rome, was recorded the first structure used concrete mixture and proven of the success of Roman invention which still standing until today. In 1756, concrete was modernise by the British engineer, John Smeaton by mixing powered brick into the cement and adding pebbles as a coarse aggregate. In 1824, Portland Cement was invented by the english inventor, Joseph Aspdin by burning ground limestone and clay together which change the chemical properties of the materials and produce high quality of cement. It became the first true artificial cement ever produce and re mained its production until today. 20 years later, the parisian inventor, Joseph Monier invented reinforce concrete, which are the combination of concrete and steel which produce the tensile or bendable strength of metal and the compressional strength of concrete to withstand heavy loads (C.L. Page And M.M. Page, 2007). Classification of Cement Cement are categorise as two (2) categories which are Hydraulic Cement and High Alumina Cement. Hydraulic Cement is the cement that set and hardened under chemical reaction. Its can be classified into Natural Cement, Aluminious Cement and Portland Cement. The most used or well known is the Portland Cement (PC) which is high demand in market that are used in the construction and building industries or use as solution to problems for engineer. By changing or reducing or increasing the chemical properties of the compenent can produces another different types of PC and different purposed in construction industry (V.S. Ramachandran, 1984). However, theirs several types of PC are used in malaysia construction industry. Ordinary Portland Cement (OPC) at figure 2.3 (a) is the most important type of cement which commonly used in construction and building industries which can be purchase at the local building supply store. The OPC was classified into three grades, namely 33 grade, 43 grade and53 grade depending upon the strength of the cement at 28 days when tested as per IS 4031-1988. But the actual strength obtained by these cements at the factory are much higher than the specifications. In the other hand, the production of Rapid Hardening Portland Cement (RHPC) at figure 2.3 (b) is similar to Ordinary Portland Cement (ORC). This cement develops its strength rapidly which give advantages in construction industry where its development at the age of three (3) days, which give the same strength of seven (7) days development to ORC. Although, the RHPC set its development in short period, it is not known as Quick-Setting Portl and Cement (QSPC), but it is well known as High Early Strength Cement because of its development product. The RHPC are widely used in construction industry as Industrial Building System compenent such as prefabricated concrete construction where the formwork is required to be removed in early stage for other use. In other purpose of RHPC are used for road repair works, and in cold weather concrete where the rapid rate of development of strength reduces the vulnerability of concrete to the frost damage (Dr. Hanizah A.H, 1997). Fact showing that OPC is low resistance of the attack of sulphates which produces in ground soil and other particular action. Sulphate Resisting Portland Cement (SRPC) at figure 2.3 (c) give protection to the concrete from chemical attack. Therefore, it is high demand cement which hardly found at the local store rather then OPC. Their normally used at the high concentration of sulphate such as at marine condition area, in foundation and basement, fabrication of pipes which likely buried in sulphate bearing soils, and in sewage treatment or repairs works. Sulphate attack occur during the frame work of hardened cement paste which results the expansion on the paste and produce defect such cracks and subsequent disruption. Attack of the Sulphate is greatly accelerate by alternate wetting and drying which normally takes place before and after the building development which result in the future (Dr. Hanizah A.H, 1997). Quick Setting Portland Cement (QSPC) at figure 2.3 (d) indicates sets very early where setting of property is brought out by reducing the gypsum content at the time of clinker grinding. It is required to be mixed, placed and compacted at early stage and mostly used under water construction and repair work where pumping is involved which has been use during the construction of smart tunnel in Kuala Lumpur, Malaysia figure 2.3 (f). Use of QSPC in such conditions reduces the pumping time and makes it economical. QSPC may also find its use in some typical grouting operations. For manufacturing various Colored Portland Cements (CPC) at figure 2.3 (e), either white cement or grey Portland cement is used as a base because of white cement is costly. Basicly, the CPC is generally use as decorative work and its production is from mixing several percentages of pigment with portland cement which form to grey or red or brown (Dr. Hanizah A.H, 1997). Theories about concrete failure Knowledge and understanding the behaviour of the concrete or in other words Durability of Concrete are most important to the engineer or developer to prevent the concrete fail to serve its purpose as durable material. Durability of concrete is defined as its resistance to deteriorating influences which may through inadvertence or ignorance reside in the concrete itself, or which are inherent in the environment to which it is exposed.(Wood H, 1968). Previous study, proved that their are several theories causing the concrete to reduce its strength and its capability which can be either external or internal factor. The behaviour can be either physical, chemical, or mechanical which can damaged the concrete indirect or direct processes (A.M Neville, 2002). Therefore, the physical theory which causes the concrete loss its performanance which either by the effect of the high temperature or differences in thermal expansion of aggregates. Infact, the alternating freezing and thawing of concrete and the associated action of de-icing salt are the combination of physical and chemical processes which likely as contraction and expansion process where normally takes long periods of time to give its result. However, the chemical process normally take places at external area where the chemical attack mainly from the aggressive ions likely as chlorides, sulphates, or carbon dioxide, which mainly produces by the natural or industrial. Other theory was the mechanical process which either made by the abrasion, erosion, cavitation or loads impact (A.M. Neville, 1995). But however, sources of the concrete failure can be considers into two (2) factors (C.L. Page And M.M. Page, 2007):- The environment factors The production factors. The Environmental factors The environment is one of the sources which something that cannot be controlled by human or in other words known as the act of God. Therefore, these factors can be categorise as (Edward A. Noy, 2005) :- Abrasion and Erosion, Climatic Condition, Atmospheric Pollution, Biological Attack, and Chemical Attack. Abrasion and Erosion Abrasion is the running surface or namely as landslide that cause by rain which are either direct or indirect fall to the unprotected surfaces which happen on high land area. However, the definition for the erosion is commonly similar with abrasion but different in process where it occur on force motion. Therefore, these two factors can occur either by human action or forces of nature (Edward A. Noy, 2005). Climatic Condition Commonly, the most effected surface on concrete are at the exterior area on building. Therefore, the design of the concrete at exterior area must be able to withstand the conditions that produced such as the weather or temperature changes, both daily and seasonal. The processes normally end up with cracking and spalling that may cause by expansion and contraction where the process takes long period of time to produce its result(Edward A. Noy, 2005). Atmospheric Pollution Atmospheric Pollution is one of the environment source which is not a new problem where the prevention was made since King Edward II of England in 12 century until today. Therefore, world new era of technology for economical purposed which made rapid growth of industrialized buildings for instance, factories where developed without realizing the impact to the environment such as emission of acidic and alkaline agents into atmosphere that is pollutant. These two compenent can cause failures to concrete where the aggressive reaction of both agents can overtake the compenent of the concrete which result in reducing the value of the concrete and causing corrosion problem in reinforced concrete bar. These problem not only effected the failures to concrete, but its also effected the human health which can cause illness, athsma, running nose, red eyes, and also can cause death (Harris,Samuel Y, 2005). Biological Attack Generally, every building will produce this type of problem which result in the growth of algae, fungi and bacteria to the concrete. These cause by the temperature different between internal and external of building where the temperature meet at dew-point and produce moisture to the concrete which to the growth that be solve by maintenance or temperture controlled (Edward A. Noy, 2005). Chemical Attack Chemical attack is the source that made the failures to concrete where the process involve the changing of the concrete compenent either by adding or increasing or reducing its compenent. The chemical attack which produce by rain and ground soil are carried acids and sulphate compenent. Chemical attack normally react during development where reaction of acids and soft water with the hardened cement, reaction of sulphates with aluminates in concrete, and reaction of alkalis with reactive aggregates in concrete (Ransom W.H, 1981). The Production Factors The production factor is involvement of human to controlled the concrete quality. To produce quality concrete, it can be categories as followed (Edward A. Noy, 2005):- Type of cement Type of aggregates Degree of compaction Water / Cement ratio. Type of Cement At chapter 2.3 are the several types of cement and its charactistic which are use in malaysia. The proper choice of cement use is important to produces concrete to protect its compenent from overtake by other deficiencies. However, by accurate measurement or calculation, can help the concrete to serve its ability without concerning its maintenance. Table 2.1 below show the measurement or calculation of cement which has been done by previous study (Edward A. Noy, 2005). Type of Aggregates Researcher proven that durable concrete can produced by good quality aggregates that are clean and free from impurities. Aggregates is used to decribe the gravel, crushed stones and the other materials which are mixed with cement water to make concrete. These can be classify as High Density aggregates, Normal aggregates and Light Weight aggregates. High-Density aggregate are classified as high specific gravity which are likely required in exceptional circumstances. However, Normal Density Aggregate specificed gravity between about 2.5 and 3.0 such as crushed rock, sand and gravel and broken bricks which happened in natural (Concrete Society, 1989). For the Light Weight Aggregate are the partical density or dry loose bulk density of less than 2000 kg/m3. Therefore, materials which can be considers as light weight aggregate are pumice, foamed lava, volcanic tuff and porous limestone which happened naturally. However, materials required processing which occurs naturally such as expanded clay, shale and slate are also consider as light weight aggregate. Other material which still consider as ligth aggregates such as sintered pulverised fuel ash (fly ash) aintered slate and colliery waste, foamed or expanded blast furnace slag that produce from industrial (Edward A. Noy, 2005). Degree of compaction Compaction or Vibration to the mixing concrete before drying process in progress are very important to prevent the failure not only to the concrete which also to the structure. The purposed of these method are to reduce the air which trapped during placing the concrete and to prevention of honeycomb on the concrete surfaces. Air contained inside concrete is about 5% every 75mm slumped and concrete with a 25mm slump may contain as much as 20%. If fully compaction or proper vibration procedure is made, concrete can result in strong, impermeable and durable otherwise, durability will be drastically reduced due to air voids in the concrete. As calculation was made, every 1% air contain in the concrete can reduce more than 5% loss of strength to the concrete and also reducing the bonding between concrete and reinforcement (A.M Neville, 2002). Water/Cement ratio As the engineering done the practice on the workability which are commonly conducted before applying it to the building as it compenent. One of the workability factor was water cement ratio which proven the most improtant part in producing quality concrete. Mixing of concrete should be applyed with lowest w/c ratio as possible and tested with compaction methods as mention previously inorder to produces durable and ability concrete. In engineering researches in german labratory, the practicles of the ratio give different spaces. The higher w/c ratio give more workability to the concrete compared to the lowest w/c ratio. Although, the high w/c ratio gives advantage on workability but it can reduce the concrete ability and effecting the hardening process at the early stage which can produce deficiencies to the concrete in the future. Therefore, figure 2.5 shows the differences spacing between cement practicles in different w/c ratio. Defect on Concrete As mention before, the sources of the concrete failure are from the environment factor and the production factor that been described at 2.4 and 2.5. The effects of these factor gives defect to concrete which are majority resulting in cracks. Some of the defects can be identified immediately and some cannot be recognised. As building surveyor, recognising defect and decision making on the problems are difficult part mostly to unidentify defect or unexplainable problems. Some of the solving method can be costly such as defect occured on foundation which effecting the structure compared to the defect occur to the concrete which can be easily done by owner himself. Figure 2.6 shows the identification of typical types of cracking to concrete surfaces which cause by this factors which has been study before. Deformation of the Surface Three defects cause deformation of the concrete surface, but may not exhibit any other symptoms. The first is curling or warping. This is the deformation of the edges and corners of a slab-on-ground in the absence of any loads. When caused by moisture, this deformation is called warping; when caused by temperature, it is called curling. The second defect is the delamination of surface mortar from underlying concrete. It is difficult to visually observe a delamination before it becomes dislodged from the surface. However, in small discrete locations, the surface may exhibit convex rising called blistering. Blisters are generally isolated, but may be closely spaced and can combine to form a large blister or delamination. A third defect occurs when isolated low spots on the surface collect water and have no means of drainage. These surface water pools are known as birdbaths. Cracking of the Surface Cracks appear in concrete for many reasons. Some cracks can appear as secondary symptoms of other defects, such as a long rounded crack following the structural failure of a warped slab. Discussed here are cracks that are primary symptoms of distress, caused by volume changes and structural failure. Shrinkage cracks have many different looks and can be e difficult to distinguish from cracks caused by other mechanisms. Discreet, parallel cracks that look like tearing of the surface are caused by shrinkage while the concrete is still fresh, called plastic shrinkage. Fine random cracks or fissures that may only be seen when the concrete is drying after being moistened are called crazing. This defect may also become evident when a translucent coating is applied to the concrete surface. Cracking that occurs in a three-point pattern is generally caused by drying shrinkage. Large pattern cracking, called map-cracking, can be caused by alkali-silica reaction within the concrete. Structural failure cracking may look like many other types of cracking; however, in slabs they are often associated with subsequent elevation changes, where one side of the crack is be lower than the other. Disintegration of the Surface Disintegration of the surface is generally caused by three types of distress. When laitance forms on the surface, it is called dusting. This can be caused by a number of reasons, which include carbonation of the surface by unventilated heaters or by applying water during finishing. Raveling or spalling at joints occurs when aggregates or pieces of concrete from the joint edges are dislodged. The last form of disintegration is the breaking of pieces from the surface of the concrete generally caused by delaminations and blistering. Popouts are conical fragments that come off the surface, typically leaving a broken aggregate at the bottom of the hole. Popoffs, or mortar flaking, is similar to popouts, except that the aggregate is not broken and the broken piece is generally smaller. Flaking of the concrete surface over a widespread area is called scaling. Types of cracks Popoffs, or mortar flaking, is similar to popouts, except that the aggregate is not broken and the broken piece is generally smaller. Flaking of the concrete surface over a widespread area is called scaling.