Properties of Concrete Containing Recycled Aggregates - Lab Report Example

Coordinator Properties of concrete containing recycled aggregates The prime aim of this study was to investigate the effect of recycled aggregates on compressive strength of concrete and the effect of recycled aggregates on indirect tensile strength of concrete. The data was collected using the compressive strength test, slump test, and indirect tensile test. The study found out that the recycled aggregate had no effect on the slump value. The strength value of the concrete cube was affected whenever an amount higher than twenty percent was added. The strength of the indirect strength of tension reduced faster when over thirty percent of the aggregate was added. The study concluded that the percentage of the recycled aggregate increased with the decrease in the strength of the concrete. Introduction To date, there has been an increasing interest and demand in aggregates starting from the industrial by products, non traditional sources, and the recycled demolition and construction wastes. The Pozzolan and the recycled aggregates are some of the concrete that have recently gained popularity in the construction industry (Smith 3). The pozzolan is an aluminous and siliceous material that posses none or little cementations value. In water or in a finely separated form, the material chemically reacts with calcium hydroxide to give out compounds with cementations traits. This may happen at normal temperatures. The artificial and natural pozzolan material is used as supplementary materials of cementations. In any cases, the artificial pozzolan could be made in a deliberate manner through the thermal activation of the clays kaolin to give the metalaolin. In other cases, the material can be obtained as a byproduct from the processes of high temperature like the fly ashes given out by the production of the coal fire electricity. The industrial by-products like the metakaolin, burned residues of organic matter like rice husk, fly ash, and fume silica obtained from smelting of silicon are commonly used pozzolans. The use of these pozzalans is reported to be well established in different countries (Smith 15). Supplying high quality by products of pozzolan has limitation since many local sources have been fully exploited. Different alternatives to the pozzolanic by product should be realized to expand the range of the byproducts of the industry and to increase the usage of the pozzolans. In some locations, the natural pozzolan may be found in abundance. This material is used as a Portland cement addition in countries like Germany. A significant portion of the natural pozzolan used in many countries has a volcanic origin. The pumices, volcanic ashes, are mostly used since they are deposits having altered volcanic glass. The volcanic glass is changed to zeolites through interacting with alkaline liquid like water. The sedimentary deposits are not common. On the other hand, the recycled aggregates are reused construction or industrial by-products, which were once considered as wastes or rather damped. The material is produced through screening, and crushing the previously used concrete structures and concrete. In other cases, the asphalt may be crushed to obtain the aggregate. In many cases, the reclaimed aggregates may be used as base materials for sidewalks, roads, and the slabs. Some examples of the recycled aggregates include the recycled concrete from demolition material waste and construction, reclaimed aggregate from scrap tyres and asphalt pavement. These are the concrete aggregates that are made from crushing the sound and cleaned waste demolition of about ninety five percent concrete weights. The aggregated have a total contamination level below one percent of the mass bulk. The different material that could exist in recycled aggregates include crushed stones, grave, hydraulic cement. Recycled aggregate could be used for many applications such as a road base. Using recycled aggregate is important because it can save a huge amount of money for the purchasers and the local government. It creates a number of increased business opportunities, sales on the recycling energy, conserve the scarce resource of the urban aggregates and assist the local government in meeting the goals of diversion. This paper reports on a study done to investigate the properties of concrete containing recycled aggregates. Method Apparatus The material and apparatus used in this study include split cylinder test machine, 3 x 100 mm cube, 150 x 300 mm cylinder, curing Tank, polythene sheeting, small concrete mixer pan, weight recorder balance, 1.8kg of Water 11.4kg of Coarse Aggregate, 6.1kg of Sand, and 3.6 kg of Cement. Procedure A small quantity of the concrete was mixed by the group. There was a control mix that had virgin aggregates. The virgin aggregates included 11.4kg Coarse Aggregate, 6.1kg Sand, and 3.6kg Cement. In addition, three mixes were prepared with different quantities of recycled aggregates. These (course aggregates) were replaced at 10, 20, 30, 40 & 50% with recycled aggregate. This meant that 10% mix contained 1.14kg recycled aggregate. The concretes were mixed by a small mixer pan. About 3 x 100 mm cubes and 150 x 300 mm cylinder were casted. A slump test was performed before the casting. After this, labels were placed on the cylinders and cubes then they were covered with polythene to avoid the drying out of the concrete. After two to three days, the cube moulds were striped by the technician and the hardened cubes stored in water inside the curing tank. At particular ages, the cubes were removed from the tank and weighed immediately in water and air to find out their density. The cubes were then loaded in a standard way and the maximum compressive load identified. The concrete cylinders were loaded across the diameter at the particular ages using a split cylinder. The split cylinder was used to determine the indirect tensile strength of the given concrete. This was calculated using the equation ft = 2P (N/mm2) /πDL, where P = failure load in Newtons (N) D = diameter of cylinder = 150 mm, L = length of cylinder = 300 mm. The collected data was recorded in the table under the results section of this report Results The obtained values were recorded in table 1,2,3,4, 5, and 6 respectively. The values were recorded in accordance to the percentages of the recycled aggregate that replaces the aggregate of the natural coarse material. . Table 1: Virgin aggregate Cube No. Max Load Strength Age (kN) (N/mm²) (days) 1 245.0 24.50 7 2 233.9 23.39 7 3 302.8 30.28 14 4 300.9 30.09 14 5 347.4 34.74 21 6 361.7 36.17 21 7 367.4 36.74 28 8 369.8 36.98 28 Mean 316.1 31.6 17.5 Standard deviation 50.98334 5.098334 7.826238 Max Load (kN) Cylinder: 188.9 Table 2 : Course aggregates at 10% Cube No. Max Load Strength Age (kN) (N/mm²) (days) 1 187 28.73 7 2 294.6 29.46 7 3 355.8 35.58 14 4 344.7 34.47 14 5 381.2 38.12 21 6 369.5 36.95 21 7 372.4 37.24 28 8 370.8 37.08 28 Mean 347.0 34.7 17.5 Standard deviation 34.05888 3.405888 7.826238 Max Load (kN) Cylinder: 186.9 Table 3: Course aggregates at 20% Cube No. Max Load Strength Age (kN) (N/mm²) (days) 1 254.2 25.42 7 2 261.6 26.16 7 3 343.2 34.32 14 4 330.0 33.00 14 5 342.5 34.25 21 6 352.1 35.21 21 7 375.8 37.58 28 8 377.4 37.74 28 Mean 329.6 33.0 17.5 Standard deviation 44.1393 4.41393 7.826238 Max Load (kN) Cylinder: 185.8 Table 4: Course aggregates at 30% Cube No. Max Load Strength Age (kN) (N/mm²) (days) 1 250.2 25.02 7 2 259.6 25.96 7 3 340.2 34.02 14 4 337.0 33.70 14 5 339.5 33.95 21 6 347.1 34.71 21 7 372.8 37.28 28 8 375.4 37.54 28 Mean 327.7 32.8 17.5 Standard deviation 44.31633 4.431633 7.826238 Max Load (kN) Cylinder: 190.9 Table5: Course aggregates at 40% Cube No. Max Load Strength (kN) (N/mm²) 1 215.9 21.59 2 212.3 21.23 3 248.3 24.83 4 279.7 27.97 5 300.2 30.02 6 301.3 30.13 7 317.6 31.76 8 319.3 31.93 mean 274.3 27.4 Standard deviation 40.71151 4.071151 Max Load (kN) Cylinder: 180.9 Table 6: Course aggregates at 50% Cube No. Max Load Strength Age (kN) (N/mm²) (days) 1 210.0 21.00 7 2 212.6 21.26 7 3 225.6 22.56 14 4 228.6 22.86 14 5 280.6 28.06 21 6 284.7 28.47 21 7 290.5 29.05 28 8 294.4 29.44 28 mean 253.4 25.3 17.5 Standard deviation 34.84432 3.484432 7.826238 Max Load Cylinder: (kN) 171.2 Discussion According to the results, for the cubes, the tensile strength of the concrete was relatively higher than the control values. The tensile strength decreased as the percentages increased. The highest tensile strength was at 10 % whereas the lowest tensile strength was at 50 %. For the cylinder, the load values were higher than the control values. The trend of the load values for the cylinder decreased steadily with a high value at 30% (190.9) and the lowest value at 50% (171.2). This means that recycled aggregate had no effect on the slump value. The strength value of the concrete cube was equally affected whenever an amount higher than twenty percent was added. The strength of the indirect strength of tension reduced faster when over thirty percent of the aggregate was added. This study showed that the percentage of the recycled aggregate increased with the decrease in the strength of the concrete. The plotted graphs showed a linear trend with a positive gradient for all cases. This is in line with the theoretical values. In essence, concretes have a high compressive strength and a lower tensile strength. This enables the concrete be reinforced by materials having a stronger tension (Paul, Benjamin & Glenn 7). Washer. The concrete elasticity may be constant at reduced tress levels, but may reduce at high levels of stress. Concretes do have a reduced thermal expansion coefficient, and shrinks when it matures (Smith 16). All structures of concrete may crack as a result of the tension and shrinkage. The concrete that are subjected to a load for a lengthy duration of time may be prone to creep (ACI Committee 318 21). The concrete density varies, but in most cases, may be about 2400kg/m3. In this case, without any compensation the concrete may fail as result of stress. This means that the elements of concrete that are subjected to the stresses of tensile needs to be reinforced with the materials hang strong tension. Conclusion The study found out that the recycled aggregates have a reduced tensile strength in comparison to other concrete. All the objectives of this study were achieved. The experimental values showed a similar trend to that of the theoretical values with little variations. The observed variation in the experimental data was because of experimental errors. Some of this errors include the errors due to air resistance, faultiness of the apparatus, errors as a result of wrong calculation, approximation errors, and parallax. These experimental errors could be avoided by performing the experiment three times and taking an average of the experiment to avoid the errors due to parallax. The experiment can be done in a room with vacuum condition to avoid the interference of the air resistance. The apparatus should be checked to confirm their accuracy before the onset of the experiment. This would help in minimizing the experimental errors (Smith 16). Work Cited Paul, Fuchs., Benjamin, Graybeal & Glenn, Washer., The elasticity Properties of the concrete. Deutsche Gesellschaft Fur Zerstorungsfreie Prufung. 3 (2007): 14-17. ACI Committee 318. ACI 318-08: Building Code Requirements for Structural Concrete and Commentary. American Concrete Institute., 4(2008): 21-30 Smith, Greg. Concrete certification company American Standard Testing admits it faked safety and inspection reports on thousands of New York City buildings, New York: Jack and Sons 2012. Print. Read More