MODELS FOR PREDICTING THE STRUCTURAL CHARACTERISTICS OFSAND-QUARRY DUST BLOCKS

ABSTRACT

In this work, models for predicting six structural characteristics and cost of sand-quarry dust blocks  were  developed.  Three  model  equations  namely  Scheffe’s  simplex  lattice design (pseudo component), Scheffe’s simplex lattice design (component proportion) and Osadebe’s  model  were  developed  for  each property.  The  properties  investigated  were Compressive strength, Water absorption and Split tensile strength. The others are Static modulus of elasticity, Flexural strength and Shear strength. The models were fitted to data obtained from tests on various mixes of 140 sand-quarry dust hollow blocks of 450 x 225 x

225 mm, 66 beams of 600 x 150 x150mm and 66 cylinder specimens of 150mm diameter and 300mm long. Adequacy of the models were confirmed using F statistic and normal probability plot. Computer  programs,  were developed  to determine  the  responses  to a given mix and the mixes  that give a desired  response  value.  The  effect  of the partial replacement of sand with quarry dust on the characteristics of the blocks was also studied. Component interactions was studied using Cox response trace plots. Comparisons between the experimental and model predicted results and  between the models were made. The percentage difference between the experimental and model predicted values were all below

5% for all the models and responses. The analyses also show that there is no  significant statistical  difference  between  the  models.  The  minimum  and   maximum  values  of compressive strength predictable by Scheffe’s pseudo component model are respectively

2.74 and 5.22Nmm-2.  The corresponding values for the water absorption of the blocks are

3.21  and  7.84%.   For  the  Scheffe’s   component   proportion   model,  the   predictable compressive strength values range from 2.77 to 5.23Nmm-2. The corresponding range for water  absorption  is  3.20  to  7.84%.  The  minimum  and   maximum  flexural  strength predictable   by  the  Scheffe’s   pseudo   component   model   are  2.40   and  4.34Nmm-2 respectively.   The  corresponding   values  for  the  Split  tensile  strength  are  2.24  and

3.33Nmm-2. For Scheffe’s component proportion model, the corresponding values are 2.45

and 4.35Nmm-2   for the flexural  strength and 2.27 and 3.33Nmm-2   for the split  tensile strength.  Analyses  of the pseudo  component  models show that there is  binary synergy between  sand  and  quarry  dust  for  all  the  properties.  Other  binary  combinations  anti synergistic  effects.  Cement  and  water  has  the  greatest  effect  on  the  properties.  The structural properties of the blocks improved  when 10 to  40% of the sand was partially replaced  with quarry dust. The optimum  replacement  was at 40% with an increase  in compressive strength of 27%. A list of 117 mixes that meet NIS 87: (2004) recommended

minimum  compressive  strength  of  3.45Nmm-2   for  load  bearing  sandcrete  blocks  was established.    It  is  recommended  that  the  inclusion  of  quarry dust  in  sandcrete  block production  be  encouraged  especially  in  areas  where  quality  sand  for  sandcrete  block production is scarce and expensive.

CHAPTER ONE INTRODUCTION

1.1    General

Walls are the basic element in the construction of most buildings. They are often required to be load bearing, especially in low rise buildings (1-2 upper floors).  Sandcrete blocks are the most commonly used unit in wall construction  in modern  Nigeria and, indeed,  the entire  West  Africa.  The  use  of  laterite  and  other  forms  of  walling  units,  for  the construction of modern residential buildings have not made much progress when compared to the use of sandcrete blocks. The same can also be said of bricks. The major advantage of sandcrete blocks is the ease of production and laying of the blocks

The  structural  properties  of  blocks  of  interest  include  compressive  strength,  flexural strength, water absorption, modulus of elasticity, shear modulus and split tensile strength. Others are density, fire resistance, durability and thermal conductivity.  These properties are dependent to a very large extent on the relativeproportions of the constituents and the method of production process.

Sandcrete  blocks  are traditionally  made  of cement,  natural river sand  and water.  The constituents  are  mixed  and  placed  in  a  mould  which  is  removed  immediately  after compaction and leveling of the top. The newly produced blocks are self-supporting; hence they are often referred to as zero slump concrete. Individual blocks are joined together, after curing, to form walls using cement-sand mortar. It is often the practice to partially replace the sand portion with other materials such as laterite, coarse aggregate or quarry dust. Sand-quarry dust blocks are sandcrete  blocks  in which the sand portion has been partially replaced with quarry dust.

1.2      Statement of the problem

There has been a growing interest recently, especially in the developing countries, in the use  of quarry  dust  (or quarry rock  dust)  in  the  production  of concrete  and  masonry products. This is partly as a result of the unchecked depletion of the natural sources of fine aggregates (river sand) which has resulted to an increase in their  price (Sekar et al, 2011, Ilangovana  et  al,  2008,  Devi  and  Kannan,  2011)  and     environmental  degradation (Khamput, 2006, Jayawardena and Dissanayake, 2006). Many sand mining sites have been closed because of the damage they cause to the environment. For example, a popular sand mining site within the campus of the Federal University of Technology, Owerri, Imo State of Nigeria was closed because of the environmental degradation resulting from the river sand mining operations. Another site close to a major culvert on the Otamiri River along Aba road, Owerri was also closed for the same reason.

The problem of scarcity of good fine aggregate in some areas has been exacerbated by the ever increasing demand for concrete and masonry products. Attempts have been made to either  partially  or  completely  replace  sand  with  other  materials  in  the  production  of concrete and masonry products. Such materials have included laterite and quarry dust. The problem of sand scarcity is of great  concern that some  equipment  manufacturers  have

developed  rock crushing equipment  that produce “manufactured  sand” whose  gradation closely resemble that of natural river sand (Norman 2008, Hudson, 1997).  Quarry dust should be differentiated from manufactured sand in that unlike quarry dust, manufactured sand is purposefully made to resemble the gradation of the sand through washing, sieving and blending of the quarry waste (Cement Concrete and Aggregates Australia, 2008).

The great infrastructural development in many countries, Nigeria inclusive, has led to the establishment of many rock quarry sites, resulting in the production of great  volumes of quarry dust. Quarry dust is a by-product of the rock quarrying process whose size ranges from below 63 micrometers to 5 millimeters (< 63µm – 5mm). It  generally has a large proportion of its particle being far less than 2.36mm in size.  Only a little portion of quarry dust produced is utilized. Its major use is as a filler material in base and wearing courses in roads. Use must therefore be found for the greater portion remaining in order that it would not constitute another environmental  hazard. It is this need to utilize the excess quarry dust, and to reduce the need for natural river sand that has led to it (quarry dust) being used in full or partial replacement for natural sand in concrete, sandcrete block and in soilcrete block production. The use of quarry dust is further encouraged when it is noted that some engineering properties of concrete and masonry products are improved when quarry dust is used as partial replacement  for natural river sand Sekar et al, 2011, Nanda et  al, 2010, Oyekan and Kamiyo, 2008, Falade, 1993).

One area of interest in which the use of quarry dust has been tried is in the production of sandcrete blocks where it has been used partially to replace sand. In this regard answers must be provided to such questions as:

(i) what is the effect of the inclusion of quarry dust on the structural properties of the blocks?

(ii) what percentage of quarry dust is optimal to achieve the desired value of a

response?

(iii) what is the cost implication of incorporating quarry dust in sandcrete blocks?

The effect of the inclusion of quarry dust in sandcrete block production has been partially addressed by some researchers (Boeck et al. 2000, Oyekan and Kamiyo 2008, Olaniyan et al. 2012, Danso 2005). In their works, it was confirmed that the inclusion of quarry dust did improve the compressive strength, but at varying degrees. A replacement of not more than 40% of the sand was suggested by Danso (2005).

Works on quarry dust utilization in sandcrete block production has centered mainly on the determination  of  their  compressive  strengths  and,  occasionally,  on  the   hygrometric characteristics.  Not much has been done on other parameters such as Static modulus of elasticity, flexural strength, split tensile strength and water absorption which are also very important in structural designs. Such properties of blocks need also be investigated  and documented.

Mix proportioning is of great concern as it is well known that the properties of concrete and its related products are greatly influenced by the proportions of the  constituents.  A desired property of the block can only be achieved through a proper mix design. Many mix design methods have been developed over the years for concrete but not much exist for sandcrete blocks. The use of empirical methods and the application of existing concrete design methods (for example, ACI: 211.3 (1987)) to sandcrete block mix proportioning is, to say the least, wasteful and uneconomical. This is even worse with the introduction of quarry dust in the mix. The use of  existing research works are often not helpful as the information  are sometimes  not  properly documented.    Many researchers  often  do  not specify unambiguously the amount of water or the water/cement ratios employed in their works. The use of such statement as: “Water was added as to make the mix good enough for block making”  is  very common. Such a statement  grossly neglects the well-known

effect of water/cement  ratio in concrete works and often makes replication of the  work difficult.

There are virtually no models that predict the structural characteristics of sandcrete blocks made with sand partial replacement with quarry dust. The need for such models cannot be overemphasized as they will be of great help in mix proportioning byreducing the time and cost of conducting trial mixes.

1.3      Statementof Objectives

The objectives of this work will be to:

1     investigate  the  effect  of  partial  replacement  of  sand  with  quarry  dust  on  the structural characteristics of sand-quarry dust blocks.

2     develop mathematical models that can predict the structural characteristics of sand- quarry dust blocks.

3     establish mathematical relationships, if any, between the compressive strength and the other properties of sand-quarry dust blocks notably water absorption, flexural strength, split tensile strength and modulus of elasticity.

4     develop  models  for  predicting  the  production  costs  of  various   sand-quarry dustmixes and blocks.

5     study  component  interactions  of  sand-quarry  dust  blocks  through  the  various models developed

6     present the result of the various models developed in such a way that they can be readily used in commercial sand-quarry dust block production.

1.4 Scope of Study

This  work  will  be  limited  to  the  formulation  of  model  equations  for  predicting  the structural characteristics of sandcrete blocks with the sand partially replaced with quarry

dust. The replacement will range from 10 to 40% with the cement/combined  aggregate ratio ranging from 1: 6 to 1: 10. Three model mixture experiment forms will be considered notably:

    Scheffe’s simplex lattice model (pseudo component model),

     Scheffe’s simplex lattice model (component proportion model)

    Osadebe’s model.

The  structural  properties  investigated  will  be  limited  to  compressive  strength,  water absorption, flexural strength, split tensile strength, shear strength and static  modulus of elasticity. All tests will be on hardened specimens.

1.5   Justification of Study

1.  The study will provide additionally needed data on use of quarry dust in  block production.

2.  The  mixes  developed  for  block  production  will  be  of  great  help  in  assisting commercial block producers in meeting required strength targets.

3.  The models that will be developed will be of great assistance  in mix design by forming the basis of trial mix designs, thus eliminating great experimental works and the high cost often associated with such ventures.

4.  The models that will be developed will be of great help in optimizing constituents of sand-quarry dust blocks to meet a desired property.

5.  The cost models will be of great use in optimizing the cost of sand-quarry dust blocks.

6.  The  relationships  formulated  between  the  compressive  strength  and  the  other properties will be of great help in making estimates for these properties since, most times, the compressive strength is the only property tested for.

₦5,000.00 – DOWNLOAD FULL PROJECT DOWNLOAD FULL PROJECT Added to cart

---

---

---

---

Related Project Topics :