Reuse of Construction and Demolished Concrete Waste by Producing Affordable High Strength Concrete Block

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1 Reuse of Construction and Demolished Concrete Waste by Producing Affordable High Strength Concrete Block. NTITANGURANWA Jean paul 1,a*, KABANO James 1,b and GASINGWA Noel 1,c 1 Civil, Environmental and Geomatic engineering, University of Rwanda, Kigali, Rwanda a Kabdul424@gmail.com, b jameskabano@gmail.com, c gasingwanoel@gmail.com Abstract: The issue of achieving sustainable environment is highlighted in different national and international strategic documents, such as Rwanda Viosion 2020, EDPRS II and MDGs. Rwanda on its track towards achieving sustainable environment, is still experiencing some challenges like Environmental degradation for the search of aggregates, energy for extraction of natural aggregates and difficulties in finding dumping sites for demolitions and construction wastes. Therefore, all those problems have created the need for developing a new source of construction materials. The idea of recycling of C&D concrete wastes aims at finding solution to the environment degradation caused by damped demolished wastes as well as producing affordable high strength concrete blocks. This research investigated the availability of C&D concrete wastes and it was discovered that up to 33.33% of C&D waste came from concrete structures while more than 23.75% of people confirmed to have been involved in demolition works more than three times a year.the research was done by collecting sample composed of C&D concrete wastes at construction site of BPR headquarter where they demolished the existed building for construction of a new multistory building in kigali city and the sample was crushed, batched and mixed with a proportion of 1:3 and 1:5 as stated by Rwanda Bureau of Standards and manufactured new concrete blocks. The research performed on series of concrete blocks: 2 series each made of different proportions of cement for recycled concrete blocks, and one serie of reference blocks made of natural aggregates. Compressive strength test gave an average of 5.13N/mm 2 for recycled concrete block, which fulfills requirement of Rwanda Bureau of standards for hollow concrete blocks and which is 0.87 times the compressive strength of an ordinary block tested under same conditions. Finally, the cost effectiveness showed that the new recycled concrete block will be affordable by reducing at 15.6% of cost for that one made of natural aggregates. Keywords: Concrete wastes, Recycled concrete block, Mechanical properties, Cost effectiveness and Environmental protection 1. Introduction Sustainable environmental management is a topic of global concern. According to RSB Newsletter (2014) stated that Building materials account for about half of all materials used and about half the solid waste generated worldwide. These materials have an environmental impact at every step of the building process: extraction of raw materials, processing, manufacturing, transportation, construction and disposal at the end of a building s useful life. The environmental protection and promotion has been among the cross cutting issues to be tackled by our country until 2020 at minimum. Rwanda has put a lot of efforts, enforcing 1

2 measures and strategies, and large budgets on environmental management programs. However, environmental degradation is still one of obstacles to green economy. Additionally, the increased growth of construction works countrywide has resulted in the consumption of a vast amount of natural aggregates, bricks, asphalt and other construction materials sources of which are limited. Moreover, Rapid increase of construction works contributes not only to depletion of natural aggregates but also to difficulties in finding suitable landfills. Concrete waste is generally found among construction waste, demolition waste, production waste and waste returned in ready-mix trucks, and with the development of concrete construction industry its amount will only grow. The reuse of concrete could help not only in reduction of concrete landfill, but also in limitating the exploitation of natural resources. Building materials transportation costs could be reduced as well. There also exist beneficial reasons for improving the quality of materials which help to extend the life of recycled materials, especially in terms of reducing the greenhouse effect. The manufacturing of concrete blocks has been subjected to the inclusion of waste materials following intensive research work in recent years. This research focuses on seeking alternative building materials to replace the main ingredients which are currently been used in manufacturing of concrete blocks. These blocks can be used as a partial or full replacement of either cement or aggregates. By using waste, recycled and byproduct materials in the production of concrete blocks, the problems of cost and resource availability can be overcome. Furthermore, environmental pollution problems that arise from the manufacture of such materials can be minimized. Benefits also come in terms of reduced disposal costs. The production of concrete blocks as building materials for use in constructing walls has become important in developing countries. The most common criteria for concrete is high compressive strength as well as resistance to weather, impact and abrasion. 2

3 2. Experience in demolition activities 50,00 45,00 40,00 35,00 30,00 25,00 20,00 15,00 10,00 5,00 0,00 GRAPH SHOWING THE OCCURENCE OF DEMOLISHED MATERIALS Bricks& blocks concrete structures Steel structures Timber structures Figure 1: Graph showing occurence of demolished materials The graph above is showing the proportions of how demolished materials are being generated in quantity. From research carried out using a questionnaire it shows that bricks and blocks are the most generated wastes by 43.59% and concrete structures contribute 33.33% of wastes. Steel and timber don t produce much wastes they involves less than ten percent. Even though bricks and blocks represent a large quantity of demolished materials they are not totally considered as wastes since they are again reused in walling construction. Whereas demolished concrete material is mostly considered as waste. 3. Practical use of demolished materials Others Percentages During this research, apparently aimed to know the current use of C&D wastes, from the obtained data presented in the graph above shows that most of the generated C&D wastes of 65% were taken to land fill which contribute to environmental degradation. This shows a great difference with 17.5% who take advantage of reusing and recycling C&D wastes. Some people of 6.5% don t have an idea of what to do with those wastes; they are likely to take them to landfill. 3

4 GRAPH SHOWING USE OF C&D WASTES PERCENTAGES 0 Land fill Reuse on site Recycled into new materials I don t know Figure 2:Graph showing use of C&D wastes 4. Preparation of recycled concrete blocks These include resource inputs, production processes, and product (output). A sample of C&D concrete wastes was taken to TRINITAS GROUP LTD at Kicukiro to be recycled into new concrete blocks.water used during mixing is potable water from distributed water by WASAC and cement used was PPC of 42.5 Mpa in 50 kg bag manufactured by CIMERWA. Other inputs were labour, energy and information. Labour was represented by a helper and machinary technician, energy were mechanical by use of electrical machine and information includes structural requirement, age at which strength is required, concrete block specifications, standards and codes of practice. In this study, concrete blocks with load bearing capacity that produced from recycled C&D waste after 28 days of curing are focused. The load bearing capacity in Rwanda can be defined as the concrete blocks with minimum strength betwenn 5 and 7 N/mm2 if the brick or blocks are solid, or 3.5 to 5.5 N/mm2 if the bricks or blocks are hollow and load bearing (RS144). Crushing and sieving of C&D concrete wastes: At this stage C&D concrete wastes were composed by big blocks and we were required to crush them into small elements for easy and better mixing and molding. Crushing was done manually at production site by use of heavy hammers as shown if figure below. After complete crushing sieve was applied in order to have a uniform sample that will maintain the uniformity of manufactured recycled concrete block. 4

5 Figure 3: A picture showing crushing and sieving of C&D concrete wastes Batching and Mixing design: Batching was done using measurements by wheel barrow as normally used at construction sites. As part of our research is to produce affordable concrete block, We have done two different mixing design in order to make a comparative analysis with current applied quantity of ciment in the mix and reduced quantity of cement in the mix. TRINITAS GROUP LTD produces concrete blocks with natural sand and aggregates with a mixing design of 1:3. One bag of cement 50 kg of 42.5Mpa. Based on that we decided to make the first mixing design the same as that in order to see the difference if the same quantity of cement is applied on different types of materials. Second Mixing design used was 1:5 where ahalf of cement used in the first mix were used. 5. Manufacturing of blocks The mechanical compaction machine was applied because it is expected to give higher load bearing capacity and aesthetics of the block. It is the method which is commonly used by professional concrete block producers in Rwanda. The concrete blocks were covered with a plastic sheet for 24 hours to prevent rapid hardening. After 24 hours, the concrete blocks were cured in water (immersed) for 26 days. Then they were taken out of the water for surface drying for one day before the laboratory testing. Figure 4: A picture during manufacturing of recycled concrete block 5

6 5.1. Laboratory testing of recycled concrete block After the 28 days of curing, the concrete block specimens were taken to the laboratory at RTDA laboratory for testing. The density, water absorption ratio and compressive strength were tested. The analysis was carried out according to the standard methods which are specified in Rwandan standards. The following is a summary of how the analysis was carried out. Compressive strength test: The concrete block specimen was placed and centered on the Platen of a compression testing machine. The compaction machine (MFL System-PRUF UND MESS) with a maximum of 3000 kn was used. The gross area of the loaded surface was length-width i.e. 400x200 (mm) bed face. Two soft sheets of plywood were placed under and above the specimen to reduce friction. The compressive strength result reported is an average over 9 specimens of three different mixing designs. The compressive strength was calculated as shown below. C = a S a a a Eq.1: Computation of compressive strength Density: Concrete block specimens were weighed by SOEHNLE-Wagebereich 0.5 bis 55 kg and the dimensions were measured by veneer caliper with 50 cm and 100 divisions. The density was calculated using equation below. For each sample type, the average of the 3 specimens was calculated: D= a H Eq.2: Computation of Density Water absorption ratio: Firstly, blocks were dried in the oven ( o C) for 24 hours and then cooled at room temperature for about 4 hours and then weighed. After that, they were immersed in water for another 24 hours. Then, they were dried (surface drying, enhanced by towels - absorbent cloths) and weighed. The water absorption ratio was calculated by using equation below and the average results of the 3 specimens on each sample were calculated. W= a y a y a % Eq.3: Calculation of water absorption ratio 5.2. Results for concrete block produced from recycled C&D waste The recycled concrete blocks were produced by using Sand and fine aggregates from the sample of recycled concrete wastes. After 28 days of controlled conditions of curing, the concrete blocks were taken to the laboratory for testing. The compressive strength, water absorption ratio, and density were measured and the results are shown in Figure. The results showed that the compressive strength of recycled concrete wastes block range from 4.07 to 5.25 N/mm 2 but Blocks produced by natural sand aggregates have compressive strength ranging between 5.67 to 6 N/mm 2. The mean compressive strength of recycled concrete block (B) of mixing ratio 1:3 was found to be 5.13 N/mm 2 and the mean compressive strength for recycled concrete block 6

7 specimens (C) of mixing ratio 1:5 was found to be 4.15 N/mm 2. For the specimens made with natural sand and gravel (A), the mean compressive strength was found to be 5.87 N/mm COMPRESSIVE STRENGTH(N/mm2) DENSITY(g/Cm3) WATER ABSORPTION(%) 1 0 A B C Figure 5: showing results of concrete block B and C produced from recycled concrete wastes and A from natural aggregates. The results of the concrete blocks presented in Figure above, showed that the concrete blocks with high density value have the higher value of compressive strength. Concrete block A with density 2.083g/m 3 have a compressive strength of 5.5N/mm 2 while for C that had a lower density of g/cm 3 than others, has a lower compressive strength (4.15 N/mm 2 ). These results are generally in agreement with Fuller s theory that the higher the density, the higher the strength (Raju, 2002). The recycled concrete block C had presented the low compressive strength among others 4.15 N/mm 2 and this is due to the reason of adjusting the mixing design from 1:3 to 1:5 ratios. Furthermore, the compressive strength results proved that there is a possibility to recycle the concrete wastes and masonry rubble into building materials because the recycled concrete blocks produced in 100% recycled concrete wastes materials with a mixing design of 1:3 gave the compressive strength falling into the accepted range by Rwandan Bureau of Standards(RS144) Cost effectiveness of recycled concrete block against natural raw materials concrete block The estimation of cost showed that one unit of recycled concrete block made of C&D concrete wastes experiences the cost of Rwf while the one made of natural sand and aggregates costs Rwf.. Based on these findings it is clearly seen that recycled concrete block made of C&D concrete wastes is affordable since it can save 62.5 Rwf which is 15.56% of cost for one concrete block. We believe that the cost of Rwf can even be decreased more if a crushing 7

8 machine is used during crushing of C&D concrete wastes, for the cost estimations was based on the manual crushing method used in this research. 6. Conclusion The main purpose of this research project was to conduct a study on the reuse of demolished waste concrete materials by producing an affordable and high strength concrete blocks. This research confirmed the availability of C&D concrete wastes where around 33.4% of demolitions are of concrete structures and around 24.0 % of interviewed professionals are involved in demolition activities more than three times a year. Through the manufacturing and laboratory testing of recycled concrete block, it was established that the compressive strength of recycled concrete block falls in the accepted range of Rwandan Bureau of standards where the results was between (N/mm 2 ) with an average of 5.13 N/mm 2. The Rwanda Bureau of Standards considers load bearing hollow concrete blocks as one in the range of 3.5 to 5.5N/mm 2. This research shows that there is a huge demand of concrete blocks for walling in construction industry in Rwanda where around 34.5% of walling works is done by concrete blocks. The cost estimation of recycled concrete block was found to be much affordable with the cost of Rwf per one block compared to Rwf of concrete block made of natural aggregate. Reuse and recycling C&D concrete materials conserves landfill space, reduces the environmental impact of producing new materials, and can reduce overall building project expenses through avoided purchase/disposal costs. Reference [1] Robert, B. & Mehmet, C., Application of Construction and Demolition waste for improving Performance of Subgrade and Sub-base layers. IJRRAS, Volume 12, pp [2] Shiran, J., Performance of Recycled Concrete Aggregates As Granular [3] Jayakody, S., Gallage, C. & Kumar, A., Assessment of Recycled Concrete Aggregates for Road base and sub -base. Kuala Lumpur, Malaysia, s.n., pp