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CEMENT STANDARD AND INCIDENTS OF BUILDING COLLAPSE: AN EMPERICAL ISSUE

CEMENT STANDARD  AND INCIDENTS OF  BUILDING COLLAPSE: AN EMPERICAL  ISSUE

PROF. DR-ING. P.A. OKEREKE; PhD, REngr. MNSE, MNICE,MNIOB, FIIA, FNATE

DIRECTOR, RESEARCH AND LINKAGES, IMO STATE UNIVERSITY, OWERRI

E-Mail: [email protected]

 

ABSTRACT

The recent controversy that poor quality cement was the cause of the spate of building collapse in Nigeria as alleged by the Standards Organisation of Nigeria (SON), the Association of Block Moulders and some Civil Society Organisations on one side and the counter defence by Cement Manufacturers to the contrary on the other side, has to many keen observers, been a source of worry and a huge embarrassment to professional bodies in the built-environment. The allegation not only portrayed Nigeria as technologically backward and incapable of managing such fundamental issue of national standards, but also calls to question, the role of engineers and builders in developing national standards for construction materials and components. This is at a time when other countries are directing their efforts on nano, nuclear and space technologies. The setting up of a committee by SON to review the standards of cement at this time in our nation’s history, is like reinventing the wheel, since the standard of cement from the British Standards (BS) have been in existence since 1958, hence the inscription BS 12-1958 on all 50kg sack for Ordinary Portland Cement (OPC).   In an attempt to lay to rest this controversy, the paper looks at the issue from the perspective of a researcher, with empirical data on the properties of OPC produced in Nigeria and also data on the properties of concrete produced in Nigeria from 1985 to date. The paper compares concrete produced in Nigeria with those from other developing and developed ones, with a view to highlighting any differences and with suggestions on how to remedy the situation in the future.

Key Words: Cement, Concrete, standards, Building collapse, National Building Codes

INTRODUCTION

Recently, the Director-General of the Standards Organisation of Nigeria (SON) inaugurated a Technical Committee comprising representatives from the University of  Nigeria Nsukka, Nnamdi Azikiwe University Awka, University of Lagos, Federal University of Tecchnology, Minna, Council for the Regulation of Engineering in Nigeria (COREN), Nigerian Society of Engineers (NSE), Cement Manufactures’ Association  of Nigeria (CMAN), Manufactures Association of Nigeria (MAN), National Association of Block Moulders (NABM), Raw Materials Research and Development Council (RMR&DC), Nigeria Building and Road Research Institute (NBRRI), and some key cement manufacturers in Nigeria ( Dangote, Unicem,and Ibeto), Julius Berger, and representatives of some unnamed Civil Society Organisations in the country.

What is interesting is the composition of the “technical committee” which is almost competing with the on-going National Delegates Conference recently inaugurated by President Jonathan, except with the absence of representatives of traditional rulers and religious organisations. One is therefore at a loss to understand what qualifies it as a technical or expert committee without the members of  the building profession who by virtue of the National Building Codes are statutorily meant to play major roles in the incidents of   collapsed buildings. I mean members of the Nigerian Institute of Building (NIOB) and its regulatory body, Council of Registered Builders of Nigeria (CORBON). The absence of these bodies which in line with the National Building Codes are the most users of cement blocks and take major responsibility in the construction of buildings and by implication, the incidents of collapsed buildings in Nigeria, underscores the importance of the exercise and its intended outcome.    

According to the D-G of SON, Dr. Joseph Odumodu, the “Technical committee is to review standard framework in the production of cement to ensure that no sub-standard cement is produced in the country”. The setting up of this committee was as a result of the disagreement among the stakeholders- the Civil Society Organisation; blocks moulders on the one hand and the cement producers on the other hand. According to the former, the existence of the 32.5grade cement instead of the higher 42.5 grade was responsible for the incessant cases of collapsed buildings in the country, while cement manufacturers, specifically Dangote and WAPCO insist that their products even the 32.5 grade is not responsible for incidents of collapsed buildings. Defending this view, the Chief Executive Officer of WAPCO, Mr. Joe Hudson averred that the standard of cement being produced in the country was good, and that the problem of building collapse was not that of cement, but a problem of enforcement of proper building standards and code of practice. I cannot but agree more with Mr. Hudson for reasons to be adduced in due course.

For an organisation such as SON which is charged with the responsibility of setting  and  maintaining standards of building materials among other products not to be sure  of the quality of materials produced by any manufacturer ab- initio in conformity with an already established  standards to turn around to accuse cement producers of producing low quality cement, is quite unfortunate. It only goes to underscore why government has not been able to find solution to the ugly incidents of collapsed buildings. It is rooted in the misnomer in official quarters of where to look for the right answers whenever a building collapsed. In most cases, the general public is deluded with sundry explanations from such professional bodies like the Nigerian Institute of Architects (NIA), the Nigerian Institute of Quantity Surveyors (NIQS), the Nigerian  Institute of Estate Surveyors and Valuers (NIESV), and even Nigerian Institute of Town, Urban and Regional Planning, etc.(Okereke, 2005). Often than not, members of these professional bodies are quick to tell the uninformed public that buildings collapsed because their members were not involved. They usually blame quacks for such mishaps without telling the public who these quacks are. It is with this general mindset, that important government agencies like SON, which should champion the efforts at seeking solutions to the incidents of collapsed buildings, have no standard procedures for setting and controlling standards in line with international best practice.

METHODOLOGY AND RESULTS

In an attempt to resolve this controversy, the paper has, using relevant empirical data from the results of many years of research on the properties of cement brands produced in Nigeria, as well as  imported bulk cement which have been re-bagged  and sold in 50kg bags, attempted to answer the following questions:                                

  1. Do the properties of cement produced in Nigeria meet international standards?
  2. To what extent is the quality of cement responsible for building collapse?
  • What is the situation in other countries, especially with respect to technologically advanced countries?
  1. What is the true position here in Nigeria, with respect to cement quality and building collapse and the way foreward?

THE IMPORTANCE OF CEMENT IN CONSTRUCTION

Concrete is the basic materials used in the construction of structures, including buildings, bridges, and other infrastructural facilities. It is a conglomeration of cement, water and aggregates (fine and coarse). Obviously, cement is the key ingredient in the production of concrete, as it is responsible for binding together the other ingredients, as such determines to a large extent the strength of the concrete.(Cemex, 2012) As a matter of fact, cement alone takes more than 3% of the total cost of a building (Petrov, 2008). According to Russian experts, cement is the bread of modern construction (NISI,1987). The significance of cement in ensuring the stability, durability and to an extent, the adoption of cost-effective technology for timely completion of any structure, is to say the least overbearing. The entire process of adapting new techniques based on recent advances in science and technology has to take into consideration, the properties and quality of the available cement.

Results from research findings (Okereke, 1987), show that the quality of cement can influence the following:

  1. Increase in the productivity of precast concrete yard or factory;
  2. The ease with which construction is carried out;
  • The speed with which structures (buildings, bridges, etc.) are accomplished;
  1. Increase in the productivity of labour in the placement and compaction of concrete into position;
  2. Increase in the durability of structures, and
  3. Improvement in the homogeneity of concrete.

Without going into details on how cement quality influences the above enumerated accomplishments, suffice it to state that  research findings, reveal that the major factor that is responsible for the variability of concrete strength is the variability   of the strength of cement (Okereke, 2003). Without doubt, the significance of other factors such as accurate batching of ingredients, the consistency in the grading of aggregates, and their other properties like freedom from deleterious matters, etc., the homogeneity of concrete is the determinant factor.

Generally, the properties of concrete are dependent on the 4 major mineralogical compositions of the cement clinker, namely: Tricalcium silicate (3CaO.SiO2 or C3S), Decalcium silicate (2CaO.SiO2, or C2S), Tricalcium aluminate (3CaO.Al2O3, or, C3A) and Tetracacium alunmino-ferrite (4CaO.Ale2O3.Fe2O3, or, C4AF). In Table 1, is shown the major mineralogical composition of 3 most popular cement brands in Nigeria and their basic properties.

Apart from the mineralogical composition of cement, the general properties of concrete depend on the mix, that is, the respective contents of the concrete ingredients. In Nigeria, concrete mixes are usually specified in ratios (usually by volume) of the ingredients as follows:

  1. 1:11/2:3 ( for high quality concrete, such as in pre-stressed concrete);

Table 1 Mineralogical Compositions and Cement Properties in Nigeria

Cement Brand

        Mineralogical

         Composition

                 Properties

 

 

 

C3S

C2S

C3A

C4AF

Degree of Fineness

Initial    ST

Final

ST

Strength

 

(%)

(%)

(%)

(%)

   Cm2/g

(Min.)

(Min.)

N/mm2

 

I

56

15

12

   8

   3560

    65

 120

  25

 

II

46

29

  6

 12

   3600

    80

 190

  45

 

III

50

18

16

   9

   3050

    75

  130

  35

 

 

 Source : Results from Tests (2012)

  1. 1:2:4 ( for reinforced concrete);
  • 1:3:6 (for mass concrete, that is, without reinforcement);
  1. 1:x:y (x and y> 3 and 6 respective- for lean concrete, that is, concrete of less importance, such as for blinding).

The specification of concrete and its batching by ratios, especially in volumes is               improper, as it leads to the production of poor quality concrete due to  inaccurate batching of ingredients. As a result, concrete of the same mix vary considerably in their properties as shown in Table 2.

Table 2. Variability in the cube Strength of concrete of the same mix ratio (1:2:4) in Nigeria

Construct. Proj.

Sample size

     7-Day Cube Strength

 

   28-day Cube Strength

 

Mean

Variance

Coeff. of Variation..

Mean

Variance

Coeff.  of Var

 

N/mm2

N/mm2

   ( %)

N/mm2

N/mm2

      (%)

 

  A

   44

   21.5

   6.0

    27.9

   27.5

   6.1

  22.2

 

  B

   48

   16.1

   2.6

    16.1

   24.0

   2.9

  12.3

 

  C

   48

   17.6

  43.0

    24.4

   24.9

   3.9

  15.7

 

  D

  260

   23.7

    4.8

    20.3

   29.4

   6.5

 

22.1

 

  E

  100

   15.2

    0.76

      5.0

   24.1

   1.33

 

5.5

  F

 108

  23.8

   8.25

   34.6

   30.2

  5.47

 

18.1

 

  G

   84       

  18.6

   6.38

   34.3

   20.9

  5.48

   26.2

 

  H

   24

  25.7

   8.48

   32.9

   30.4

  8.19

   26.9

 

  I

 100

  17.5

   1.2

     6.9

   26.7

  1.11

      4.15

 

  J

 636

  18.0

   3.83

   21.3

   24.7

  4.35

   17.6

 

  K

 100

  25.4

   1.88

     7.4

   29.8

  3.25

   10.9

 

 

Source: Results from Research (1985-2010)

The reasons why concrete mix in ratio is not recommended where strength is of importance include the following:

  1. Inaccurate batching of ingredients due to subjective factors and non-consideration of the moisture content, especially in the fine aggregate;
  2. Production of non-homogenous concrete, due to variability in the contents of the various ingredients, most especially water and aggregates contents;
  • Production of concrete with very high coefficient of variation, not only in the strength of concrete, but also in the basic properties of concrete such as density and the rate of water absorption.

The high degree of variability as depicted in Table 2, where the coefficient of variation is between 4.15-26.9% is due to the following reasons:

  1. Inconsistency in the actual quantity of ingredients (cement, sand, gravel and water);
  2. Use of cement with variable strength characteristics;
  • Inconsistency in the mixing time and method of mixing;
  1. Variability in climatic conditions at the time and place of concreting, and;
  2. Variability in the technology of preparation, transportation and placement of the concrete into position.

From the data in Table2, the characteristic cube strength of concrete produce across Nigeria could be computed using the expression (Okereke, 2008):

                             fcu =                                              ……..(1)

where,

 is the mean 28-day cube strength of concrete study sample produced in Nigeria;

          the mean standard deviation of the study sample and

          1.64- statistical constant.

After substituting the computed values from Table 2 in Eq.(1), the characteristic cube strength of concrete produced in Nigeria was found to be 19.4N/mm2. This is less than the usually specified (designed) strength of 20N/mm2 for 1:2:4 concrete mix usually used by structural engineers in reinforced concrete design for most residential buildings across the country. This could be explained as one of the reasons why buildings collapse is high in Nigeria, that is, the production of concrete of low quality in spite of the fact that most cement brands used in the country are of the Ordinary Portland cement (OPC) type.

According to a foremost British expert in concrete, J.D. McIntosh, MSc, FICE, FIStrutE, FIOB,FISTC of the Cement and Concrete Association, Wexham Springs. Slough, Bucks (2010), OPC is adequate for most purposes. Where special properties are required, he opined, rapid-hardening Portland cement may be used to attain strength at an earlier age or offset low temperatures.0n the other hand, low heat PC might be used for mass concrete, where a lower rate of evolution of heat during hydration is desirable, and the accompanying lower rate of development of strength is acceptable.     

 Generally, Portland cement (PC) is classified under two main groups, namely:          i) Portland cement without any additional minerals (under this group falls Ordinary Portland cement (OPC) and Rapid         Hardening Portland cement (RHPC), and  ii)  PC with some additives to improve on some of the properties of the cement. Under this group are Pozzolanic Portland cement (PPC) and Portland Blast Furnace cement (PBFC) suitable for specific purposes.

PC is classified according to its characteristic strength of 25, 35, 45 and 55N/mm2, that is, if its maximum resistance when subjected to compressive load applied over a surface area of F=250mm2 as OPC, RHPC and ERHPC respectively. Thus, based on the average strength of six samples, cement can be classified as in most international standards in the following grades: G25, 35, 45 and G55 (ACI, 2002). These presumably, are the equivalents of SON’s 32.5 (G35) and 42.5 (G45). By this, SON and the National Assembly with its recent Bill on the regulation of cement grades are saying that OPC is not good enough in Nigeria as according to them, it is the cause of the incidents of collapsed buildings. What a fallacy and show of ignorance of cement standards!

In Table 3 are shown the respective grades of concrete with their cement contents and grades in most developing, European Union countries and the USA, for comparison.

In practice, the maximum possible strength concrete capable of being produced is 40N/mm2 with cement contents of 450-580 of grade 45 (42.5). Such concrete grades usually have plastic consistency (slump) of between 3-5cm with coefficient of variation of between 13 and 22% (ACI, 2002).

Table 4: Comparative Analysis of Cement/Concrete Quality

Quality Parameter

Unit

Developing

countries

EU Countries

United States of America

 

Mean strength

N/mm2

250

  37.2

   48.6

Max. Strength

N/mm2

  40

  45.0

   65-80

Average cement content

kg/mm3

270

  –

    –

Average water content

%

    8-10

  28-30

  25-26

Coefficient of variation

%

10-20

    9-13

   4-9

 

Source: Research Result (2010)

CONCLUSION AND RECOMMENDATIONS

The procedure adopted by SON in determining the actual quality of cement produced in Nigeria runs counter to international best practice. All that it needed doing was to request cement manufacturers to furnish it with the following information regarding their products:                                                                                       i)  the chemical composition (that is, the 4 major mineralogical compositions of the cement clinker);

  1. ii) the basic properties of the cement ( initial and final setting time, the strength characteristics (tensile and compressive);

 iii) the volume constant  and the heat of hydration in accordance with  British Standard (BS 12: 1958) specifications for Portland cement or its Nigerian equivalent ( NIS 444:13:2003).

Armed with this information, SON can then verify them in their own laboratory without wasting tax payers’ money to convene another national conference on cement. That is the practice all over the world. An alternative recourse would have been to organise a broad based national conference with invitation thrown open to members of the academia (not selected institutions without any basis as has been wrongly done), relevant professional bodies, the industries and stakeholders in the built-environment.  The theme of such a conference could be: Evolving National Standards for the Built-Environment, with a wide range of sub-themes covering the various major building materials such as steel, timber, paints, roofing sheets, etc., which also lack authentic National standards. The outcome from such a conference can further be fine-tuned by a real Technical committee comprising sub-committees of experts in the related fields. Such a conference is long overdue.         

Cement in the Nigerian market comes from two main sources: locally produced and imported. Hitherto, until Dangote Group ventured into cement production, the major cement manufacturers were Nigercem, Nkalagu, ,established as far back as in 1957,  West African Portland Cement Company (WAPCO), Ewekoro in 1960, Benue Cement Company (BCC), Gboko, and later, others came on board with locations in Ukpilla, Sokoto, Calabar, etc, under various brand names. Among the major brand names of imported cement are Eagle Cement, Ibeto, Atlas, BUA, and others spread across the country. These brands of cement (local and imported), are sold in 50kg sacks. Each bag carries the label:  Portland Cement (BS 12:1958), implying that they met the requirements of Portland cement type as covered by BS 12 of 1958, with its Nigerian equivalent of NIS 11:74 (NIS 444:13 2003).

The bone of contention as to whether cement grade 32.5 is sub-standard and therefore responsible for building collapse is neither here nor there. As has been shown with empirical data and from expert opinion, OPC, with a characteristic strength of 25N/mm2 is quite adequate for most types of concrete works, including reinforced concrete and sancrete blocks. In fact, this grade of cement has been in use since 1957 when Iddo, Lagos was constructed without any adverse effect reported (Hughes and Ridley, 1958).

Nothing can be far from the truth and a huge embarrassment on our collective intelligence for anybody to state publically that houses in Nigeria collapse because the cement used in block making are of grade 32.5 .Suffice it to state categorically, that the issue of building collapse goes beyond the strength of cement. As has been pointed out, even the use of higher cement G45, is no guarantee that a building will not collapse. Scientific studies both here and in other countries show that the most preponderant factors in building collapse are incorrect structural analysis and design, wrong interpretation of drawings and specifications leading to incompetent implementation of structural details and specifications (Emma-Ochu, 2012). For example, the use of cement of higher grade cannot guarantee the production of good quality concrete, or sancrete blocks.

 Preliminary research findings on the properties of sancrete blocks produced in Imo state for instance, show that there is so much disparity in the properties of sample blocks from a total of more than 100 major blocks moulders across the state (Uche, 2014). This is due to many factors, among which are: location, climatic conditions, method of production, type of cement and sand, mix proportion, and the quantity and quality of the mixing water. The bottom line of the problem of producing good quality blocks/concrete lies in compliance to appropriate building standards and codes of practice which unfortunately do not exist in the country. I make bold to state that there are no appropriate standards in Nigeria. What we have are adopted foreign standards which are not based on local conditions, such as climate, low level of technical know-how and competence of industry operators, etc.

As a remedial measure towards reducing incidents of building collapse for the interim, the following measures are recommended:

  1. SON to convene as a matter of urgency, a national conference on construction materials with a view to establishing authentic national standards of major building materials;
  2. State chapters of NICE and NIOB to set up joint committees to establish local standards for sancrete blocks and concrete production and to monitor their compliance in order to reduce the incidents of building collapse;
  • State governments to legitimize the implementation of the National Building Codes (NBC);
  1. Mechanism to be put in place to ensure full implementation of the National Building Insurance Act (2006).

 

 

REFERENCES

American Concrete Institute (ACI) (2002). Building Code Requirements for Structural Concrete (318-05) and Commentary (318R). Farmington   Hills  MI,USA, 430pp

 Cemex (2012). Concrete Characteristics, Sweet Haven Publications.

Emma-Ochu,C. (2012). A Post Mortem of Incidents of Building Collapse in Imo State. MSc Project submitted to the Department of Building, Imo State University.

Federal Republic of Nigeria, National Building Code (2006). 1st ed. Lexis        Nexis Buttersworth.

Federal Republic of Nigeria, National Building Insurance Act (2003), National Assembly, The Three Arms zone, Abuja.

Hughes, T.(1962). Concrete Strength in West Africa. Note No. 12,WABRI, Accra.

McIntosh, J.D. (1973).Properties and Production of Concrete. Overseas Building Notes No. 153 (Information on Housing and Construction in Tropical and Sub-tropical Countries), Cement and Concrete Association, Wexham Springs, Slough, Bucks.

Okereke, P.A. (1987). Improving the Technology of Concrete Works, Using Chemical Admixtures, for the Climatic Conditions of Nigeria. PhD Dissertation, submitted to the Specialised Council on Technology and Management, Bulgarian Academy of Science, Sofia.

Okereke, P.A. (1991).Optimal Concrete Mix Design for Tropical Climate.         International Journal of Housing Science and its Application. Vol. Florida State University, Cable Island, Miami, USA.

Okereke, P.A. (2003).Construction Materials: Testing and Quality Control in Tropical Climate. Crown Publishers, Owerri.

Okereke, P.A. (2005).Due Process and Incidents of Collapsed Buildings in Nigeria: Professional Responsibilities. Proceedings, NICE National Conference, Akure.

Okereke, P.A. (2008).In-situ Quality Control of Concrete in Nigeria. Environmental Research and Development Journal, Faculty of Engineering and Environmental Sciences, Imo State University, Owerri. Vol.I, No 2:

Okereke, P.A. (2013).Investigation of the Properties of Cement Brands in Nigeria. Preliminary Research  Report, Seminar Series, Faculty of Environmental Sciences, IMSU, Owerri/

Petrov, L. (1987). Users’ Quality of Cement in Building Production. National              Research Institute, Sofia, Bulgaria.

Ridley, T (1957). High Strength Concrete.ACI Paper No. 6310, London.

Uche, F.I.(2014).Assessment of the Properties of Sancrete Blocks Produced in Owerri Metropolis. A Preliminary Research Report, Seminar Series, Faculty of Environmental Sciences Seminar Series, IMSU, Owerri.

 

 

 

 

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