SUSTAINABLE CONCRETE MADE FROM RECYCLED AGGREGATES

Transcription

1 International Journal of Civil Engineering and Technology (IJCIET) Volume 7, Issue 3, May June 2016, pp , Article ID: IJCIET_07_03_024 Available online at Journal Impact Factor (2016): (Calculated by GISI) ISSN Print: and ISSN Online: IAEME Publication SUSTAINABLE CONCRETE MADE FROM RECYCLED AGGREGATES Dr. Ing John K. Makunza Department of Structural and Construction Engineering University of Dar es Salaam, Tanzania ABSTRACT Construction and demolition waste constitutes a major portion of total solid waste production in the world, and most of it is used in land fills. One way of profitable use of wastes is the possibility of treating and reusing as aggregates in new concrete. In this paper, construction and demolition Wastes, have been studied for effective utilization in concrete. The study objective was to determine the quality of recycled aggregate such as the crushing value, absorption, density, attainable grade of concrete, and establishing the structural properties of the fresh as well as hardened concrete. The study was achieved by doing different tests on the recycled aggregates, Specimens preparation and assessment of properties of concrete in both fresh and hardened states. Most of the test results of properties of recycled aggregates have not met the minimum requirements suggested by codes, but the grade of concrete intended to be achieved was met. In conclusion, it has been found that recycled aggregates are suitable in making concrete. Also some barriers on the use of recycled aggregates have been identified, such as lack of awareness, and non-existence of specifications/codes for guiding the reuse of aggregates in new concrete. Cite this Article: Ing John K. Makunza, Sustainable Concrete Made From Recycled Aggregates, International Journal of Civil Engineering and Technology, 7(3), 2016, pp INTRODUCTION Debris from collapsed concrete and masonry structures is currently thrown away as wastes within the city of Dar es Salaam. Concrete wastes are generated when a structure fails and collapses due to overload or deterioration. In addition to that, concrete wastes can be generated when there is a change in design of a certain old building where by the old one has to be demolished so that a new designed structure can be constructed, and when structures are demolished to pave a way for expansion of roads, airports, etc editor@iaeme.com

2 Ing John K. Makunza According to Mfinanga [1], continuous industrial development poses serious problems of construction and demolition wastes disposal. Whereas on the one hand, there may be shortage of natural aggregates for production of new concrete, on the other hand the enormous amounts of demolished concrete wastes from deteriorated and obsolete structures creates severe ecological and environmental problem [2]. Preservation of the environment and conservation of the rapidly diminishing natural resources should be the essence of sustainable development. In developing countries, construction and demolition wastes have been left without proper treatment, deemed that its production is small and may not cause significant environmental degradation. However it does by altering the ph of the surface and ground water, increasing total suspended solids, reducing water clarity and random heaps of construction and demolition concrete debris alongside streets or even on water lodged areas The Problem Dar es Salaam city is the Tanzania s largest city and major administrative, commercial, industrial and transportation centre. The city s population grew from 128,742 in 1957([3], to the current population of around 4.5 million people. Due to this high population growth there is high demand of land for settlement of the people, while the government needs to expand the existing roads so as to meet the demand of the population, by doing so a lot of unplanned houses have to be demolished to pave way for the new roads and buildings such as shown the one in Figure 1 situated at Kariakoo Dar es Salaam[4]. Figure 1 New buildings replacing the demolished old ones Due to the scarcity of landfills, high cost is incurred to dispose this concrete wastes, and also environmental problem is posed due to the dumped concrete wastes. So to cater for these problems, concrete debris can be used to produce recycled aggregate that can be utilized in making concrete Objectives of The Study The objective of this study was to explore the suitability of recycled aggregates produced from construction and demolished concrete debris in making structural concrete. Basing on this main objective, the specific objectives were: To determine the quality of recycled aggregate such as crushing value, absorption and density editor@iaeme.com

3 Sustainable Concrete Made From Recycled Aggregates Establish the structural properties of the fresh as well as the hardened concrete Establish the grade of concrete that can be attained Significance of The Study Advantages of this study include the followings Recycled aggregates are low priced than natural aggregates hence good housing (Low cost buildings) with reduced rate of consumption of natural resources. Concrete debris recycling leads to substantial quantity of waste being diverted from landfill into beneficial resource generating income to the community. Decreased workload to local authorities whose resources in management of wastes is meager, enhanced environmental cleanness and decreased rate of degradation. 2. REVIEW ON CONCRETE MATERIALS The word Concrete comes from a Latin word Concretus, Meaning grow together according to the Concise Oxford Dictionary 10 th Edition[4]. This is a good name for this material because the chemical hydration process of cement and water causes the mixed material to grow together from moldable plastic to hard rigid solid. It is one of the important building materials playing part in most if not all building structures for it is possible to be molded into different shapes required for various structural elements. Concrete is durable and fire resistant when specifications and construction procedures are properly adhered to. The ingredients of concrete are coarse and fine aggregates and binder (cement) mixed with water and sometimes additives, allowed to set and cured to form a stiff and hard substance during construction of concrete structures. Recycled aggregates originate from construction and demolition debris that has been removed from pavement foundation, or buildings that has been crushed to produce recycled concrete aggregates. In Africa most construction and demolition is recycled as backfill subject to regular flooding areas. Wood nails, bricks and other materials of direct use are also reclaimed from construction and demolition for use in other construction projects Quality of Materials and Good Practices The quality of concrete produced on site, depends on the quality of materials which have to meet the minimum specifications set by codes. On top of it is know-how of all personnel involved in the production of concrete. Neville [5] in his book Properties of concrete had the following to say: Bad concrete is often a subsistence of the consistence of a soup, hardening in a honey-combed, non-homogeneous mass is made simply by mixing cement, aggregates and water. Surprisingly, the ingredients of a good concrete are exactly the same, and it is only the know-how, often without additional costs of labour, that is responsible for the difference. This is to say that principles of good concrete production should be adhered to. Concrete ingredient materials should be of the required quality and quantity. Several codes have been developed to guide towards production of good concrete in different ways, example CP110 and BS8110 [6] (Structural use of concrete), and BS 12620[7] (aggregates) and BS EN [8] (Cement). Interpreting these codes, various manuals and books have been printed. Aggregates are classified as natural or artificial aggregates [7], according to rocky type like basalt, according to fragmentation like natural or artificial processes and the editor@iaeme.com

4 Ing John K. Makunza particle size like coarse aggregates which are retained on a 4.75 mm and fine aggregates (sand) which passes through a 4.75 mm standard test sieve Recycled Aggregates Recycled aggregates originate from construction and demolition debris and consist mainly of crushed concrete and crushed asphalt pavement. Reusing and recycling of construction and demolition wastes are among the principle of sustainable construction that advocate creation on operation of health built environment based on resource efficiency and ecological principles. Reuse refers to using an object again, either of its original purpose or for a similar purpose, without significantly altering the physical form of the object or material. Recycling means using wastes as material to produce a new product. This involves altering the physical form of an object or material and making a new object from the altered material. Recycled concrete aggregate could be produced from; Recycled precast element and concrete cubes after testing, and Demolished concrete buildings such as the debris shown in Figure 2. Figure 2 Concrete debris from demolished building Whereas in the former case, the aggregate could be relatively clean, with only the cement paste adhering to it, in the later case the aggregate could be contaminated with soil, bricks and tiles, sand and dust, timber, plastics, cardboard and paper, and and metals. Fong et al (2004)[9] advocates that the contaminated aggregates after separation from other wastes, and sieving, can be used as a substitute for natural coarse aggregates in making concrete. As with natural aggregate, the quality of recycled aggregates, in terms of size distribution, water absorption, abrasion resistance, aggregate crushing value, etc. also need to be assessed before using the aggregate. 3. EXPERIMENTAL METHODS AND RESULTS The investigation work was carried out by firstly paying site visit to places where by individual peoples are involved with the production of recycled aggregates and sells them for income generation as depicted in Figure 3. Materials were sampled and tested for their suitability. Mix design was then done and specimens were prepared, editor@iaeme.com

5 Sustainable Concrete Made From Recycled Aggregates cured and tested for compressive and tensile strength. Details on the investigation work are as given below: 3.1. Sampling Of Concrete Debris Elements As the wastes that are generated in construction sites consist of bricks, blocks, concrete, reinforcements and timbers pieces, this project was limited to cement composite wastes such as Figure 3a Concrete debris crushed into aggregates Concrete and blocks. Therefore the concrete wastes had to be separated from the other debris. Aggregates for this study were obtained from crushed concrete cubes and cement/sand blocks from demolished walls of School of Law that was in vertical extension work and from broken concrete seats known as vimbwete. Figure 3b Local people crushing big concrete debris into aggregate sizes The materials were cleaned to remove soil and silt contamination, weak substance such as pieces of wood and humus. The demolished concrete boulders were in large sizes, so they had to be manually crushed using hammers into small aggregate sizes which were suitable for testing in the building materials laboratory. The aggregates were tested for grading as shown in graphic form in Figures 4 to 6. Then the aggregates were tested for their suitability such as water content, water absorption, editor@iaeme.com

6 %age Passing %age Passings Ing John K. Makunza aggregates crushing value, ten percent fines value and gross density. The results of aggregate tests are presented in Table 1. Table1 Summary of materials test results Material Test Results Specification value Sieve test FM = Crushed Concrete Moisture content 1.0% ACV 23% <45% Gross density 2.5g/cm 3 Water absorption 3.6% 0.1 4% Sieve test FM= Crushed Blocks Moisture content 1.3% TFV 30kN Gross density 2.5g/cm 3 Water absorption 11.4% 0.1 4% Fine Aggregates Moisture content 1.2% (Sand) Sieve test FM= Gross density 2.5g/cm 3 Grading Curve for Recycled Aggregates Sieve size [mm] Figure 4 Grading for recycled aggregates With regard to Figure 4, 95% of all recycled aggregates had sizes ranging from 9.5 mm to 37.5 mm Sand Grading Curve Sieve size [mm] Figure 5 Grading of sand The tested sand as depicted in Figure 5, had particles sizes ranging from 0.08 mm to 1.18 mm covering almost 85% editor@iaeme.com

7 %age Passings Sustainable Concrete Made From Recycled Aggregates 100 Resultant Curve and Target Curve Resultant Curve Target Curve Sieve size [mm] Figure 6 Resultant and target curves Cement As the quality of cement is guaranteed by manufactures, no tests were made on it at all. The type of cement that was used in this study was Blended Portland Cement R Concrete Mix Design Mix proportioning refers to the process of determining the quantities of concrete ingredients with the objective of meeting the minimum requirements for strength, durability and workability. It involves the determination of aggregates blend, amount of binder (cement) and amount of water required to make the paste. There are two methods commonly used to determine aggregates blend namely; an analytical method and a graphical method. In this study the mathematical method was used where by proportions of coarse and fine aggregates to blend to dense combination were determined. Then mix design calculations were done while observing the minimum requirements such as characteristic strength of hardened concrete, cement content, variability of the mix due to variation of quality of materials and batching. The uniformity production was assumed to be good, the size of site was taken to be small that requires a foreman and that the concrete is not more than 5% defective. Specimens Preparation Proportions of concrete ingredients were calculated using data obtained from aggregate tests. Concrete cubes, prisms and cylinders were produced using aggregates from crushed concrete as well as crushed blocks aggregates. The designated grades of concrete were C25, C20 and C15, since these are the most common grades of concrete that are applied in the construction of concrete structures in Dar es Salaam. Cubes compressive strength was tested at the ages of 3, 7 and 28 days while the prisms and cylinders were tested after attaining the age of 28 days Concrete Tests and Results Workability Test Fresh concrete was tested for its workability and consistency by performing the Slump test. The results showed that the slump value was medium as it was ranging from 30 mm to 60 mm. The obtained fresh test results are shown in Table editor@iaeme.com

8 Density [kg/m³] Desnity [kg/m³] Ing John K. Makunza Compressive Strength of Concrete The compressive strength test of concrete was done when the concrete specimens reached the ages of 3, 7 and 28 days. Results for 3 days and 7 days are normally used to assess the strength development of concrete while the 28 days age strength is taken as the final strength of concrete applicable in service condition. Figure 7 Testing of concrete cube Tests on the specimens were done at the Building Materials Laboratory of the University of Dar es Salaam. A test setup for the cube specimens in the machine is indicated in Figure 7, and the analyzed test results are shown in Figures 8 and Tensile Strength Test (BS :2000) The tensile strength of concrete can be determined by different methods such as direct tensile test, flexural (bending) strength test and tensile splitting test. In this study, bending and splitting tensile strength tests were adopted due to their simplicity in the test procedures. Test results obtained for crushed concrete and crushed blocks aggregates for tensile strength and E Modulus of the concretes are presented in Table 2. The E-Modulus values obtained are almost a half of the code values for normal aggregates concrete. In the same table fresh and hardened concrete test results such as slump values and density are also shown Densities of Crushed Aggregates Concrete 2300 Densities of Concrete From Crushed Blocks 2350 C C C15 C Age [days] Age [days] Figure 8 Compressive strength of recycled and crushed blocks aggregates concrete Figure 9 Densities of recycles Aggregates concrete editor@iaeme.com

9 Sustainable Concrete Made From Recycled Aggregates Table 2 Flexural, splitting strength and E- Modulus (prisms and cylinders) Concrete Gross Density Bending Tensile Strength Tensile Splitting Strength E- Modulus Concrete Slump Coarse Aggregates Day Days Days Grade mm kg/m 3 kg/m 3 kg/m 3 N/mm 2 N/mm 2 kn/mm 2 Crushed Prism Concrete Cylinder Crushed Prism Blocks Cylinder Percentage strength development of concrete cubes compared to Target mean value and characteristic strengths have been analyzed and presented in Table 3. Table 3 Percentage strength development of cubes compared to target mean and design characteristic strength. Material Concrete Grade N/mm 2 3 Days Strength % (Standard 35-50) 7 Days Strength % (Standard 60 73) 28 Days Strength % (Standard 100) Target % f cu % Target% f cu % Target% f cu % Crushed Concrete Crushed Blocks With reference to Table 3, it is evident that the strength development of concrete made from recycled aggregates behaves very well as it meets the specifications indicated by target values for crushed concrete at all ages. But for crushed blocks, the 28 days target strength could not be reached. The low strength may be caused by the low strength of aggregates as their aggregate crushing value (ACV) was higher than the maximum recommended value from the code. These results trend agree with the strength values presented in graphic form in Figure Discussion on the Results The average compressive strength of 26.8 N/mm 2 obtained for Grade 25 crushed concrete is less than the target strength of 34.8 N/mm 2. However, the average is greater than the required concrete grade; the low strength may be due too much water during mix as can be depicted by the slump of 60mm which is the upper limit for medium workability. Applying research experiment relationship between compressive strength and splitting strength (f t = 0.464C.f c 2/3 ), it can be shown that with the same ratio one can achieve a target compression strength of 32.7N/mm 2 if the slump is 35 mm. Compressive strength test performed on the cubes have shown compliance with the specifications at 28 days. Cubes were designed to meet characteristic strengths of 25 and 15N/mm 2 from the target mean strengths of 34.8 and 24.8N/mm 2 respectively. The compressive strength obtained for Grade 25 was 16.8, 22.1 and 26.8N/mm 2 in 3, 7 and 28 days respectively. This shows rapid gaining of strength as compared to Table 7.1 of BS 8110: Part 2 which indicates compression strength of 16.5N/mm 2 (62%) in the seventh day of casting, a value which in this project has been reached in the third day. The cement used was Portland composite cement which behaves as a Rapid Hardening Cement. The compressive strength for Grade 15 was 17.4, 21.2 and 24.9N/mm 2 in 3, 7 and 28 days respectively editor@iaeme.com

10 Ing John K. Makunza The flexural bending strength performed for Grade 25 was also acceptable as it reached 3.3 N/mm 2 and the splitting tensile strength was 2.8 N/mm 2 respectively. The tensile stress values obtained from bending are higher than those from splitting test hence resembling properties of concrete made of natural aggregates. Modulus of elasticity of 10.2 kn/mm 2 for concrete Grade 25 is less than the recommended value in BS :1985 which ranges between 19 to 31 kn/mm 2, and E- Modulus obtained for Grade 15 was 12.3 kn/mm 2. This is 35 45% less than the designated modulus of elasticity. Concrete made up of crushed blocks were weak and did not reach the characteristic strength designated. An examination on the mode of failure of the cubes when crushed under compression machine revealed that the aggregates had crushed hence an indication that individual aggregates were weaker than concrete. 4. CONCLUDING REMARKS Basing on the results of this study and discussions made above, following are conclusions and recommendations: 4.1. Conclusions The compressive strength for 3 and 7 days showed rapid gaining of strength as compared to Table 7.1 of BS 8110: Part 2[10] which indicates the compression strength of 62% of f cu value in the seventh day of casting,, a value which was attained in the third day. The compressive strength development for Grade 15 was 17.4, 21.2 and 24.9 N/mm 2 at 3, 7 and 28 days respectively being 70%, 85% and 100%. Test performed on cubes for compressive strength for concrete made up of crushed concrete have shown compliance with the specifications. However, Cubes made up of crushed blocks have shown weakness by having high water absorption and lower crushing strength. Water absorption of recycled concrete aggregates is a bit higher than natural aggregates form the same parent rock due to the cement paste which surrounds the aggregates Recommendations Further studies should be carried out to check suitability of broken blocks for various uses such as in bases and making recycled blocks The use of recycled aggregates concrete should be encouraged to reduce consumption of natural resources, decreased workload to local authorities whose resources in management of wastes is meager. Use of recycled aggregates diverts substantial quantity of waste from landfill to beneficial resource generating income to the community. This shore up the National Poverty Alleviation strategy cluster II - Provision of Low Cost Houses. Developing of proper local standards - apart from the specifications of RILEM [11] to promote the use of concrete made with recycled aggregates is needed in order to provide guidance with regard to quality of the materials and their resulting structures editor@iaeme.com

11 Sustainable Concrete Made From Recycled Aggregates REFERENCES [1] Mfinanga Alfred, Properties of concrete made from recycled aggregates, PGD Dissertation, Department of Structural and Construction Engineering, University of Dar es Salaam, [2] Chandra S, Implication of using recycled construction and demolition wastes as aggregates in concrete, Session lead paper, International Conference on Sustainable Waste Management and Recycling, 2004, Kingston University, London. [3] Makunza J.K, Challenges In Achieving Good Quality Concrete Constructions in Africa Sub-Sahara, Paper submitted to Tanzania Journal of Engineering and Technology, College of Engineering and Technology, University of Dar es Salaam, 2015 [4] Rusibamayila M, Use of recycled aggregates for making concrete, Final Year Report, Department of Structural and Construction Engineering, University of Dar es Salaam, [5] Neville A, Properties of concrete, McGraw Hill, London, [6] BS 8110 (1997), Structural Use of Concrete, Part 1: 1997 Code of Practice for Design and Construction, BSI, London, [7] BS : Aggregates for concrete, BSI, London, 2002 [8] BS EN , Cement - Part 1: Composition, specifications and conformity criteria for common cements, BSI, London. [9] Fong Winston F.K, Jaime Y.S.K and Poon C.S, Hong Kong experience of using recycled aggregates from construction and demolition materials in ready mix concrete, International Workshop on Sustainable Development and Concrete Technology, 2002, p [10] Madan Mohan Reddy. K, Sivaramulu Naidu. D, Sanjeeva Rayudu. E, Studies On Recycled Aggregate Concrete by Using Local Quarry Dust and Recycled Aggregates, International Journal of Civil Engineering and Technology, 3(2), 2012, pp [11] Dr. P. Muthupriya, An Experimental Investigation on Effect of GGBS and Glass Fibre In High Perfomance Concrete, International Journal of Civil Engineering and Technology, 4(4), 2013, pp [12] BS :1985, Structural use of concrete for special circumstances, BSI, London. [13] RILEM (1994), RILEM Recommendations for the Testing and Use of Constructions Materials, e-isbn: , Pages: 618 Publication date: editor@iaeme.com