June 2011

Q. What is the purpose of limiting the placing temperature for mass concrete?

Answer:

To avoid thermal cracking in mass-concrete construction, engineers try to keep the difference between the peak temperature and the final stable temperature to an acceptable value such that the tensile strain capacity of the hardened concrete is not exceeded. By limiting the placing temperature well below the final stable temperature, it will help to keep this differential under control. For example, for a 20°C rise in temperature, when the placing temperature is controlled at 25°C the peak temperature is 45°C. If the ambient temperature is 35°C, the temperature differential would be 10°C instead of 20°C in case the placing temperature is the same as the ambient temperature.

Also, the control on placing temperature also helps to reduce the rate of hydration. Otherwise, high placing temperature increases the rate of hydration process so that it may increase the peak temperature as thermal heat is released in shorter period of time.

Answer provided by Vincent T. H. CHU                                
 
About the author:

Vincent T. H. CHU (朱敦瀚) is renowned internationally as walking encyclopedia of civil engineering. He is the recipient of the Ombudsman’s Award 2007 under complaint-related category and Young Engineer of the Year Award 2008 (Merit) organized by the Hong Kong Institution of Engineers. He is listed in 11th Edition of Marquis Who's Who in Science and Engineering. Hs is the author of “200 Questions and Answers on Practical Civil Engineering Work”, “Civil Engineering Practical Notes A-Z”, “Ask Vincent Chu (Common FAQ on Practical Civil Engineering Works)”, “The Underlying Reasons in Practical Civil Engineering Works”, “A Closer Look at Prevailing Civil Engineering Practice – What, Why and How” and “Mastering Different Fields of Civil Engineering (VC-Q&A Method)”. Up to date, the book is known to have spread to Asia (Hong Kong, Japan, Turkey, Philippines, Mongolia, Singapore, Pakistan, Vietnam, India, Sri Lanka, Malaysia, Indonesia), Europe (United Kingdom, Switzerland, Germany, Bulgaria, Slovak Republic, Slovenia, Span, Finland), America (The United States, Canada, Argentina) and Africa (South Africa, Nigeria, Kenya, Zimbabwe, Ghana) and Islands (Barbados and Mauritius).Recent interviews with him:

(i)Career Times (19.2.2010)
http://www.careertimes.com.hk/english/article/show_article.asp?category_id=1037&article_id=13589&title=connecting-with-the-people&listby=date&listby_id=&page=1
(ii) Recruit (26.3.2010)
http://en-gb.facebook.com/note.php?note_id=378068489397
http://www.recruitonline.com/article/ArticleDetail.aspx?article_id=25909
(iii) Apple Daly (24.3.2011)
http://hk.apple.nextmedia.com/template/apple/art_main.php?iss_id=20110324&sec_id=4104&subsec_id=15333&art_id=15104087&cat_id=11011649


May 2011

Q. What is the purpose of setting a maximum temperature for mass concrete?

Background:
As a general rule of thumb, the placement of structural concrete with a minimum dimension equal to or greater than 1 metre would be considered as mass concrete. Historically, limiting the temperature differential between the interior and concrete surface so that it is less than 20°C has been found to prevent or minimize thermal cracking. The limit on temperature difference aims at reducing excessive cracking due to volumetric change.

Answer:
The establishment of maximum temperature for mass control is twofold:

  1. The control of maximum temperature effectively means that it also controls the time taken to reach the maximum temperature and reduces the temperature differential.
  2. To avoid the effect of delayed ettringite formation.

If the internal temperature exceeds 70°C, the long term durability of some concrete could be impaired by delayed ettringite formation.

Delayed ettringite formation is a type of internal sulfate attack in concrete, which is common in many concrete elements that have been heat-treated beyond a certain temperature and have restrained the normal ettringite formation, or, in concrete which is made by a high-sulfate portland cement. Rather than normal formation of ettringite by cement hydration in the plastic state, ettringite forms at a delayed state after the hardening of the concrete. In the continued presence of moisture, components of ettringite slowly dissolves out and forms ettringite in the confined spaces in hardened paste, thereby causes expansion and subsequent stresses in the paste due to restrained expansion and this leads to the eventual cracking of concrete.

Answer provided by Vincent T. H. CHU                                
 
About the author:

Vincent T. H. CHU (朱敦瀚) is renowned internationally as walking encyclopedia of civil engineering. He is the recipient of the Ombudsman’s Award 2007 under complaint-related category and Young Engineer of the Year Award 2008 (Merit) organized by the Hong Kong Institution of Engineers. He is listed in 11th Edition of Marquis Who's Who in Science and Engineering. Hs is the author of “200 Questions and Answers on Practical Civil Engineering Work”, “Civil Engineering Practical Notes A-Z”, “Ask Vincent Chu (Common FAQ on Practical Civil Engineering Works)”, “The Underlying Reasons in Practical Civil Engineering Works”, “A Closer Look at Prevailing Civil Engineering Practice – What, Why and How” and “Mastering Different Fields of Civil Engineering (VC-Q&A Method)”. Up to date, the book is known to have spread to Asia (Hong Kong, Japan, Turkey, Philippines, Mongolia, Singapore, Pakistan, Vietnam, India, Sri Lanka, Malaysia, Indonesia), Europe (United Kingdom, Switzerland, Germany, Bulgaria, Slovak Republic, Slovenia, Span, Finland), America (The United States, Canada, Argentina) and Africa (South Africa, Nigeria, Kenya, Zimbabwe, Ghana) and Islands (Barbados and Mauritius).Recent interviews with him:

(i)Career Times (19.2.2010)
http://www.careertimes.com.hk/english/article/show_article.asp?category_id=1037&article_id=13589&title=connecting-with-the-people&listby=date&listby_id=&page=1
(ii) Recruit (26.3.2010)
http://en-gb.facebook.com/note.php?note_id=378068489397
http://www.recruitonline.com/article/ArticleDetail.aspx?article_id=25909
(iii) Apple Daly (24.3.2011)
http://hk.apple.nextmedia.com/template/apple/art_main.php?iss_id=20110324&sec_id=4104&subsec_id=15333&art_id=15104087&cat_id=11011649


April 2011

Q. What is the purpose of using circular diaphragm wall instead of rectangular diaphragm wall?

Circular diaphragm walls are characterized by not converging freely when loaded externally. Consider a thin circular wall subjected to an axisymmetrical pressure. The reaction to the external pressure induces a compressive hoop force in the wall which resists the tendency to converge. The hoop force is equal to the applied external pressure x radius of circular diaphragm wall. No extra support (i.e. struts and tiebacks) is required to balance the external forces and this accounts for structural stability of circular walls provided that the hoop force does not exceed the limits of the material properties. This avoids complicated construction procedures involving coordination between excavator and anchor installer.

Also, the stable circular diaphragm walls require reduced need for embedment to provide wall stability and the embedment for mechanical stability of toe is unnecessary. On the other hand, as the hoop force provides a stiff continuous support to the circular diaphragm wall, the reaction forces (i.e. bending moment and shear force) in the diaphragm wall remain generally small leading to small reinforcement ratio.

Answer provided by Vincent T. H. CHU                               
 
About the author:

Vincent T. H. CHU (朱敦瀚) is renowned internationally as walking encyclopedia of civil engineering. He is the recipient of the Ombudsman’s Award 2007 under complaint-related category and Young Engineer of the Year Award 2008 (Merit) organized by the Hong Kong Institution of Engineers. He is listed in 11th Edition of Marquis Who's Who in Science and Engineering. Hs is the author of “200 Questions and Answers on Practical Civil Engineering Work”, “Civil Engineering Practical Notes A-Z”, “Ask Vincent Chu (Common FAQ on Practical Civil Engineering Works)”, “The Underlying Reasons in Practical Civil Engineering Works”, “A Closer Look at Prevailing Civil Engineering Practice – What, Why and How” and “Mastering Different Fields of Civil Engineering (VC-Q&A Method)”. Up to date, the book is known to have spread to Asia (Hong Kong, Japan, Turkey, Philippines, Mongolia, Singapore, Pakistan, Vietnam, India, Sri Lanka, Malaysia, Indonesia), Europe (United Kingdom, Switzerland, Germany, Bulgaria, Slovak Republic, Slovenia, Span, Finland), America (The United States, Canada, Argentina) and Africa (South Africa, Nigeria, Kenya, Zimbabwe, Ghana) and Islands (Barbados and Mauritius).Recent interviews with him:
(i)Career Times (19.2.2010)
http://www.careertimes.com.hk/english/article/show_article.asp?category_id=1037&article_id=13589&title=connecting-with-the-people&listby=date&listby_id=&page=1
(ii) Recruit (26.3.2010)
http://en-gb.facebook.com/note.php?note_id=378068489397
http://www.recruitonline.com/article/ArticleDetail.aspx?article_id=25909
(iii) Apple Daly (24.3.2011)
http://hk.apple.nextmedia.com/template/apple/art_main.php?iss_id=20110324&sec_id=4104&subsec_id=15333&art_id=15104087&cat_id=11011649

 


June 2009

Q•  What are the potential problematic areas in bell-out of bored piles?

Owing to the relatively low presumed bearing value for founding rock (i.e. 5MPa for Grade II rock with total core recovery of 85% and unconfined compressive strength more than 25MPa), it leads to the necessity to form bell-out in order to spread the pile loads in larger area, thus reducing the bearing stress at pile toes.

Firstly, in Hong Kong most of rock belongs to igneous rocks whose unconfined compressive strength is generally higher than normal concrete (no reinforcement in concrete in bell-out region). Therefore, someone may query the reason of replacement of strong rock by weaker concrete during the formation of bell-out.

When piles are concreted by tremie concrete method, soil sediments at the pile toe inside the bell-out are pushed aside and trapped in the tip of bell-out. Consequently, this would impair the functionality of the bored piles.

To maintain the stability of hanging side slope of bell-out, it requires the bell-out to be formed wholly inside sound rock. However, the rock above bell-out may be weather rock so that the hanging rock is liable to fall down and soil may collapse.

Answer provided by Vincent T. H. CH

About the author:

Vincent T. H. CHU ( 朱敦瀚 ) ( 外號 Civil 百科全書 ) obtained the degree of civil and structural engineering in the University of Hong Kong . He is the author of the column “The Civil FAQ” published in The Hong Kong Engineer published by the Hong Kong Institution of Engineers and is the author of the column “The Civil Q&A” on the website on the World Federation of Engineering Organization. He is the recipient of the Ombudsman's Award 2007 under complaint-related category and Young Engineer of the Year Award 2008 (Merit) organized by the Hong Kong Institution of Engineers. He is also the author of two engineering books, one of which titled “200 Question and Answers on Practical Civil Engineering Works” is widely publicized and posted on the websites of engineering organizations and university around the world such as Turkey, Japan, Germany, Europe, Pakistan, United Kingdom, South Africa etc. Recent interviews with him include South China Morning Post (13 March 2008), Jiu Jik 招職 (30 September 2008, link: http://www.jiujik.com/jsarticle.php?lcid=HK.B5&artid=3000022089&arttype=LEISU&artsection=CAREER ) and Face Magazine 一本便利 (2 December 2008, link:http://education.atnext.com/index.php?fuseaction=Article.View&articleID=11925677&issueID=20081203 )

 


May 2009

Q. Why do landslides occur though the rainfall has not led to full saturation in the sliding zone?

From soil mechanics, it tells us that unsaturated soils get its strength from three main components, namely, friction, cohesion and suction. In building a sand castle in a beach, experience tells us that when sand is too dry or too wet, the castle can hardly be built. However, when the sand is partially saturated, the suction (negative pore water pressure) holds the sand together and provides the strength the build the castle.

In the event of intensive rainfall, the soils cannot get away the water at the rate it is penetrating into the slope and this results in wetting up of the subsurface soils. When the slopes gets too wet (but not yet saturated), it loose much strength in terms of suction (negative pore water pressure) and results in slope failure. This occurs despite the fact that the sliding mass is well above the ground water table.

In Hong Kong about 80% of landslides occur owing to erosion and loss in suction. Only less than 20% of landslides occur as a result of increase of pore water pressure, leading to the decrease in shear strength.

Answer provided by Vincent T. H. CHU

About the author:

Vincent T. H. CHU ( 朱敦瀚 ) ( 外號 Civil 百科全書 ) obtained the degree of civil and structural engineering in the University of Hong Kong . He is the author of the column “The Civil FAQ” published in The Hong Kong Engineer published by the Hong Kong Institution of Engineers and is the author of the column “The Civil Q&A” on the website on the World Federation of Engineering Organization. He is the recipient of the Ombudsman's Award 2007 under complaint-related category and Young Engineer of the Year Award 2008 (Merit) organized by the Hong Kong Institution of Engineers. He is also the author of two engineering books, one of which titled “200 Question and Answers on Practical Civil Engineering Works” is widely publicized and posted on the websites of engineering organizations and university around the world such as Turkey, Japan, Germany, Europe, Pakistan, United Kingdom, South Africa etc. Recent interviews with him include South China Morning Post (13 March 2008), Jiu Jik 招職 (30 September 2008, link: http://www.jiujik.com/jsarticle.php?lcid=HK.B5&artid=3000022089&arttype=LEISU&artsection=CAREER ) and Face Magazine 一本便利 (2 December 2008, link: http://education.atnext.com/index.php?fuseaction=Article.View&articleID=11925677&issueID=20081203 )

 


April 2009

Q. What is the relation of pouring rate and temperature with concrete pressure on formwork?

Freshly placed concrete exerts pressure on formwork during the placing operation. It is influenced by the rate of placing and the air temperature. For instance, if the concrete pouring rate is too slow, setting of concrete starts to take place. As a result, the concrete at the bottom of the formwork sets prior to the placing of fresh concrete at the top and the maximum pressure will be reduced.

Temperature affects the rate of hydration of concrete. The higher the air temperature is, the higher will be the rate of hydration reaction. Consequently, fresh concrete tends to set at a faster rate. The pressure exerted on formwork decreases with an increase in temperature. For this reason, formwork is subjected to a higher pressure exerted by fresh concrete in winter than in summer.

Answer provided by Vincent T. H. CHU

About the author:

Vincent T. H. CHU ( 朱敦瀚 ) ( 外號 Civil 百科全書 ) obtained the degree of civil and structural engineering in the University of Hong Kong . He is the author of the column “The Civil FAQ” published in The Hong Kong Engineer published by the Hong Kong Institution of Engineers and is the author of the column “The Civil Q&A” on the website on the World Federation of Engineering Organization. He is the recipient of the Ombudsman's Award 2007 under complaint-related category and Young Engineer of the Year Award 2008 (Merit) organized by the Hong Kong Institution of Engineers. He is also the author of two engineering books, one of which titled “200 Question and Answers on Practical Civil Engineering Works” is widely publicized and posted on the websites of engineering organizations and university around the world such as Turkey, Japan, Germany, Europe, Pakistan, United Kingdom, South Africa etc. Recent interviews with him include South China Morning Post (13 March 2008), Jiu Jik 招職 (30 September 2008, link: http://www.jiujik.com/jsarticle.php?lcid=HK.B5&artid=3000022089&arttype=LEISU&artsection=CAREER ) and Face Magazine 一本便利 ( 2 December 2008 , link: http://education.atnext.com/index.php?fuseaction=Article.View&articleID=11925677&issueID=20081203 )



March 2009

Q. Why is it preferable to design stormwater drains to match soffit?

Stormwater drains collect stormwater in their corresponding catchment areas during rainstorm and convey the collected water through outlets to the sea. Therefore, in considering the hydraulic design of stormwater drains, other than normal drainage pipe capacity to be taken into consideration, one should check the backwater effect due to tidal condition at outlets if the drains are located quite close to the downstream end of outlets.

In the design of gravity drainage pipes, full bore flow capacity is normally adopted to check against the design runoff. However, one should note that the maximum flow rate does not occur under full bore conditions. The maximum discharge occurs when the water depth in circular pipes reaches 0.938D (D is the diameter of the pipe) of the pipes. Therefore, the use of full bore discharge is on the conservative side though the pipe's maximum capacity is not utilized. Similarly, the maximum velocity does not occur in full bore conditions and for circular pipes it occurs when the water depth is 0.813D (D is the diameter of the pipe) of the pipes. Hence, in checking for the maximum velocity of flow in pipes to avoid possible erosion by rapid flow, the use of full-bore velocity may not be on the conservative side.

Stormwater drains are normally designed to match soffit to avoid surcharging by backwater effect or when the downstream pipes are running full. Normally pipe size increases from upstream to downstream. For the case of matching drain invert, when outlet pipes are fully surcharged by tidal effect of the sea or when the downstream pipes are fully filled with stormwater, pipe sections immediately upstream of the outlet are also surcharged too. However, for the case of matching pipe soffit, the immediate upstream sections of outlet pipes are not totally surcharged even though downstream pipes are running full. However, it is not always practical to maintain soffit for all pipelines because it requires sufficient drop to achieve this.

Moreover, the flow of stormwater is mainly by gravity in the design of stormwater drains. In case the drains are designed to match invert, then it stands a high probability that the flow in the upstream smaller pipes has to be discharged against a head.

Answer provided by Vincent T. H. CHU

About the author:

Vincent T. H. CHU ( 朱敦瀚 ) ( 有 Civil 百科全書的外號 ) obtained the degree of civil and structural engineering in the University of Hong Kong . He is the author of the column “The Civil FAQ” published in The Hong Kong Engineer published by the Hong Kong Institution of Engineers and is the author of the column “The Civil Q&A” on the website on the World Federation of Engineering Organization. He is the recipient of the Ombudsman's Award 2007 under complaint-related category and Young Engineer of the Year Award 2008 (Merit) organized by the Hong Kong Institution of Engineers. He is also the author of two engineering books, one of which titled “200 Question and Answers on Practical Civil Engineering Works” is widely publicized and posted on the websites of engineering organizations and university around the world such as Turkey, Japan, Germany, Europe, Pakistan, United Kingdom, South Africa etc. Recent interviews with him include South China Morning Post (13 March 2008), Jiu Jik 招職 (30 September 2008, link: http://www.jiujik.com/jsarticle.php?lcid=HK.B5&artid=3000022089&arttype=LEISU&artsection=CAREER ) and Face Magazine 一本便利 ( 2 December 2008 , link: http://education.atnext.com/index.php?fuseaction=Article.View&articleID=11925677&issueID=20081203 )



February 2009

Q. Among Howe truss and Pratt truss, which is the better one from structural point of view?

Pratt truss is characterized by having its diagonal members (except the end diagonals) slanted down towards the middle of the bridge span. Under such structural arrangement, when subject to external loads tension is induced in diagonal members while the vertical members tackle compressive forces. Hence, thinner and lighter steel or iron can be used as materials for diagonal members so that a more efficient structure can be enhanced. However, under normal loading condition, the compression chord tends to be heavily loaded than tension chord at the mid-span of the truss.

The design of Howe truss is the opposite to that of Pratt truss in which the diagonal members are slanted in the direction opposite to that of Pratt truss (i.e. slanting away from the middle of bridge span) and as such compressive forces are generated in diagonal members. Hence, it is not economical to use steel members to handle compressive force. Howe truss is advantageous for usage in lightly loaded roofs where the reversal of load owing to wind may occur.

Answer provided by Vincent T. H. CHU

About the author:

Vincent T. H. CHU ( 朱敦瀚 ) obtained the degree of civil and structural engineering in the University of Hong Kong . He is the author of the column “The Civil FAQ” published in The Hong Kong Engineer published by the Hong Kong Institution of Engineers and is the author of the column “The Civil Q&A” on the website on the World Federation of Engineering Organization. He is the recipient of the Ombudsman's Award 2007 under complaint-related category and Young Engineer of the Year Award 2008 (Merit) organized by the Hong Kong Institution of Engineers. He is also the author of two engineering books, one of which titled “200 Question and Answers on Practical Civil Engineering Works” is widely publicized and posted on the websites of engineering organizations and university around the world such as Turkey, Japan, Germany, Europe, Pakistan, United Kingdom, South Africa etc. Recent interviews with him include South China Morning Post (13 March 2008), Jiu Jik 招職 (30 September 2008, link: http://www.jiujik.com/jsarticle.php?lcid=HK.B5&artid=3000022089&arttype=LEISU&artsection=CAREER ) and Face Magazine 一本便利 (2 December 2008, link: http://education.atnext.com/index.php?fuseaction=Article.View&articleID=11925677&issueID=20081203 )


 

January 2009

Q. Does the presence of rust have adverse impact to the bond performance of bar reinforcement?

In fact, the presence of rust in bars may not have adverse impact to the bond performance and it depends on the types of bar reinforcement under consideration.

For plain round bars, the rust on bars improves the bond performance by formation of rough surfaces which increase the friction between steel and concrete.

However, for deformed bars, the same theory cannot apply. The presence of rust impairs the bond strength because corrosion occurs at the raised ribs and fills the gap between ribs, thus evening out the original deformed shape. In essence, the bond between concrete and deformed bars originates from the mechanical lock between the raised ribs and concrete. On the contrary, the bond between concrete and plain round bars derives from adhesion and interface friction. With such differences in mechanism in bonding, the behaviour of bond between deformed bars and plain round bars in the presence of rust varies. Reference is made to CIRIA Report 147.

CIRIA Report 147 Care and Treatment of Steel Reinforcement and the Protection of Starter Bars pp. 11-12

Answer provided by Vincent T. H. CHU

About the author:

Vincent T. H. CHU ( 朱敦瀚 ) obtained the degree of civil and structural engineering in the University of Hong Kong . He is the author of the column “The Civil FAQ” published in The Hong Kong Engineer published by the Hong Kong Institution of Engineers and is the author of the column “The Civil Q&A” on the website on the World Federation of Engineering Organization. He is the recipient of the Ombudsman's Award 2007 under complaint-related category and Young Engineer of the Year Award 2008 (Merit) organized by the Hong Kong Institution of Engineers. He is also the author of two engineering books, one of which titled “200 Question and Answers on Practical Civil Engineering Works” is widely publicized and posted on the websites of engineering organizations and university around the world such as Turkey, Japan, United Kingdom, South Africa etc.


 

December 2008

Q. What is the effect of shear lag in a typical box-girder bridge?

Shear lag takes place when some parts of the cross section are not directly connected. For a box-girder bridge, not all parts of flanges are joined directly to webs so that the connected part becomes highly stressed while the unconnected flanges are not fully stressed. In particular, for wide flanges of box-girder bridges axial loads are transferred by shear from webs to flanges which result in the distortion in their planes. Consequently, the plane sections do not stay plane and the stress distribution in the flanges are not uniform. Moreover, there is a tendency for longitudinal in-plane displacements of bride deck away from the flange/web connection to lag behind those parts of the bridge in close vicinity to the flange/web connection.

The effect of shear lag causes the longitudinal stress at flange/web connection to be higher than the mean stress across the flange. Therefore, the effect of shear lag has to be catered for in the design of box-girder bridges, especially for those with wide flanges.

Answer provided by Vincent T. H. CHU ( 朱敦瀚 ) and Jane W. Y. YIP ( 葉穎然 )

About the authors:

Vincent T. H. CHU ( 朱敦瀚 ) obtained the degree of civil and structural engineering in the University of Hong Kong . He is the author of the column “The Civil FAQ” published in The Hong Kong Engineer published by the Hong Kong Institution of Engineers and is the author of the column “The Civil Q&A” on the website on the World Federation of Engineering Organization. He is the recipient of the Ombudsman's Award 2007 under complaint-related category and Young Engineer of the Year Award 2008 (Merit) organized by the Hong Kong Institution of Engineers. He is also the author of two engineering books, one of which titled “200 Question and Answers on Practical Civil Engineering Works” is widely publicized and posted on the websites of engineering organizations and university around the world such as Turkey, Japan, United Kingdom, South Africa etc.

Jane W. Y. Yip ( 葉穎然 ) obtained the Bachelor of Engineering Science from the University of Western Ontario Canada. Upon graduation with her first degree, she has been involved in sewage treatment project, highway structure projects, as well as stormwater drainage project.



November 2008

Q. What are the potential problems of excessive concrete covers?

From technical point of view, the effect on cracking due to an increase in concrete cover should be considered. In general, there are three main parameters which govern flexural crack width, namely tensile strain at the point considered, the distance of longitudinal bar to the concerned point and the depth of tension zone.

For the second factor, i.e. proximity of longitudinal bars to point of section, the closer a bar is to this point, the smaller is the crack width. Therefore, closely spaced bars with smaller cover will give narrower cracks than widely spaced bars with larger cover. Therefore, with an increase of concrete cover, the crack width will increase which is undesirable.

Other than the consideration of cracking, the use of cover more than required is undesirable in the following ways:

•  The weight of the concrete structure is increased by an increase in concrete cover. This effect is a critical factor in the design of floating ships and platforms where self-weight is an important design criterion.

•  For the same depth of concrete section, the increase of concrete cover results in the reduction of the lever arm of internal resisting force.

Answer provided by Vincent T. H. CHU ( 朱敦瀚 ) and Jane W. Y. YIP ( 葉穎然 )

About the authors:

Vincent T. H. CHU ( 朱敦瀚 ) obtained the degree of civil and structural engineering in the University of Hong Kong . He is the author of the column “The Civil FAQ” published in The Hong Kong Engineer published by the Hong Kong Institution of Engineers and is the author of the column “The Civil Q&A” on the website on the World Federation of Engineering Organization. He is the recipient of the Ombudsman's Award 2007 under complaint-related category and Young Engineer of the Year Award 2008 (Merit) organized by the Hong Kong Institution of Engineers. He is also the author of two engineering books, one of which titled “200 Question and Answers on Practical Civil Engineering Works” is widely publicized and posted on the websites of engineering organizations and university around the world such as Turkey, Japan, United Kingdom, South Africa etc.

Jane W. Y. Yip ( 葉穎然 ) obtained the Bachelor of Engineering Science from the University of Western Ontario Canada. Upon graduation with her first degree, she has been involved in sewage treatment project, highway structure projects, as well as stormwater drainage project.


October 2008

Q. What are the differences between epoxy grout, cement grout and cement mortar?

Epoxy grout consists of epoxy resin, epoxy hardener and sand/aggregates. In fact, there are various types of resin used in construction industry like epoxy, polyester, polyurethane etc. Though epoxy grout appears to imply the presence of cement material by its name, it does not contain any cement at all. On the other hand, epoxy hardener serves to initiate the hardening process of epoxy grout. It is commonly used for repairing hairline cracks and cavities in concrete structures and can be adopted as primer or bonding agent.

Cement grout is formed by mixing cement powder with water in which the ratio of cement of water is more or less similar to that of concrete. Owing to the relatively high water content, the mixing of cement with water produces a fluid suspension which can be poured under base plates or into holes. Setting and hardening are the important processes which affect the performance of cement grout. Moreover, the presence of excessive voids would also affect the strength, stiffness and permeability of grout. It is versatile in application of filling voids and gaps in structures.

Cement mortar is normally a mixture of cement, water and sand (typical proportion by weight is 1:0.4:3). It is intended that cement mortar is constructed by placing and packing rather than by pouring. They are used as bedding for concrete kerbs in roadwork. They are sometimes placed under base plates where a substantial proportion of load is designed to be transferred by the bedding to other members.

Answer provided by Vincent T. H. CHU and Jane W. Y. YIP

About the authors:

Vincent T. H. CHU obtained the degree of civil and structural engineering in the University of Hong Kong . He is the author of the column “The Civil FAQ” published in The Hong Kong Engineer published by the Hong Kong Institution of Engineers and is the author of the column “The Civil Q&A” on the website on the World Federation of Engineering Organization. He is the recipient of the Ombudsman's Award 2007 under complaint-related category and Young Engineer of the Year Award 2008 (Merit) organized by the Hong Kong Institution of Engineers. He is also the author of two engineering books, one of which titled “200 Question and Answers on Practical Civil Engineering Works” is widely publicized and posted on the websites of engineering organizations and university around the world such as Turkey, Japan, United Kingdom, South Africa etc.

Jane W. Y. Yip obtained the Bachelor of Engineering Science from the University of Western Ontario Canada. Upon graduation with her first degree, she has been involved in sewage treatment project, highway structure projects, as well as stormwater drainage project.

Should you have any enquiries, please feel free to e-mail us at asce@ust.hk