Research Article - (2020) Volume 0, Issue 0
The global consumption of natural sand is very high, due to the extensive use of concrete or mortar. The fine and coarse aggregates generally occupy 60% to 75% concrete volume (70% to 85% by mass) and strongly influence the concrete’s fresh and hardened properties. Now a day’s sand is becoming a very scarce material. Natural sand deposits are being depleted and causing serious threats to the environment and society. The culture of using alternative ingredients to produce materials is weak in Ethiopia. Around Jimma town, quality sand is not readily available and it is transported from Worabe, Gambella, and Chewaka that needs high transportation costs. In this situation, research began for an inexpensive and easily available alternative material to natural sand. The main objective of this study was aimed to determine the fresh and hardened properties of C-25 concrete by replacing natural sand with manufactured sand in Jimma town. This experimental study was conducted by preparing three concrete cubes for each percentage replacement. The replacement was done at 0%, 10%, 20%, 40%, 60%, and 100%. According to this study, the slump values for the above percentage replacement were 48.91 mm, 45.23 mm, 38.98 mm, 32.56 mm, and 26.14 mm respectively. The compressive strengths were 27.08 MPa, 29.34 MPa, 31.25 MPa, 27.25 MPa, and 29.22 MPa, and the flexural strengths were 3.28 MPa, 3.35 MPa, 4.37 MPa, 3.26 MPa, and 4.26 MPa respectively. The maximum compressive strength was obtained at 40% replacement with the corresponding compressive and flexural strengths were 31.25 MPa and 4.37 MPa respectively. From this result it is concluded that manufactured sand can be used as natural sand partial and fully replacement
Aggregates • Compressive strength • Flexural strength • Percentage of replacement • Manufactured sand • Natural sand
The global consumption of natural sand is very high, due to the extensive use of concrete or mortar. In general, the demand for natural sand is quite high in developing countries to satisfy the rapid infrastructure growth, in this situation, developing countries facing a shortage in good quality natural sand [1-4]. The importance of using the right type and quality of aggregates cannot be overemphasized. The fine and coarse aggregates generally occupy 60% to 75% of the concrete volume (70% to 85% by mass) and strongly influence the concrete’s freshly mixed and hardened properties, mixture proportions, and economy [5,6]. Fine aggregates generally consist of natural sand or crushed stone with most particles smaller than 5 mm (0.2 in.). Natural sand is mainly excavated from river beds and always contains a high percentage of impurities that adversely affect the properties of concrete by reducing the life of the structure .
Now-a-days sand is becoming a very scarce material, in this situation research began for an inexpensive and easily available alternative material to natural sand [8,9]. Some alternative materials have already been used as a part of natural sand e.g. fly-ash, slag limestone, and siliceous stone powder are used in concrete mixtures as a partial replacement of natural sand. However, scarcity in the required quality is the major limitation in some of the above materials. Hence, sustainable infrastructural growth demands the alternative material that should satisfy technical requisites of fine aggregate as well as it should be available abundantly [10-12]. Therefore, the main objective of this study was to evaluate the effect of percentage replacement of natural sand by manufactured sand at 0%, 10%, 20%, 40%, 60%, and 100%.
Statement of the problem
Natural sand deposits are being depleted and causing serious threats to the environment as well as society. Increasing extraction of natural sand from river beds causing many problems, losing water retaining sand strata, deepening of the river courses and causing bank slides, loss of vegetation on the bank of rivers, exposing the intake well of water supply schemes, disturbs the aquatic life as well as affecting agriculture due to lowering the underground water table are few examples [13,14].
In the present situation, the scarcity of natural sand has become a problem for the construction industry, after much research the developed technology gave rise to a new generation of sand named crushed sand or manufactured sand. Due to the booming of construction activities in Ethiopia, natural or river sand resources are increasingly depleted and its cost is becoming increasingly high [15,16]. Properties of aggregate affect the durability and performance of concrete, so fine aggregate is an essential component of concrete and cement mortar. The most commonly used fine aggregate is a natural river or pit sand. Fine and coarse aggregate constitute about 75% of the total volume. Therefore, it is important to obtain the right type and good quality aggregate at the site because the aggregate forms the main matrix of concrete or mortar [17,18].
Around Jimma town, quality sand is not readily available and it should be transported from other areas, such as Worabe, Gambella, and Chewaka which are far away from the town, it needs high transportation costs to construct building projects. Since transportation is a major factor in the delivery price of construction. This leads to additional project costs. Excavation of the sand leads to different problems like deforestation, soil disturbance, and erosion, ecological disturbance. For this reason, this research was carried out in substituting natural river sand with manufactured sand. Replacing the natural riverbed sand with manufactured sand shall be studied to pose an unquestionable issue by coming up with an excellent combination of materials for compressive and flexural strengths.
Significant of the study
This study has significant for different stakeholders. The construction parties will obtain another alternative construction material other than natural river sand with minimum transportation distance. This can reduce the overall construction project cost. The other benefit of this study is, it helps environmental protection authority by giving awareness to construction parties and then the natural disturbance to natural sand mining will reduce. It can also keep as it is the biodiversity.
Scope of the study
This research is limited to around Jimma town which is southwest of Ethiopia. The research covered determining the effects of natural sand replacement with manufactured sand of C-25 concrete properties. This experimental study only limited to 0%, 10%, 20%, 40%, 60% and 100% of replacement. In this experimental study, only some engineering properties of aggregates, slump value, and the compressive and flexural strength of concrete were done. Therefore, it did not include other properties of concrete like permeability, creep, durability, and others.
The research was conducted in the Jimma Zone, located in the south-western part of Ethiopia. Jimma Zone has a latitude and longitude of 704°’N 36°5°’E / 7.667°N 36.833°E. The climate of the Zone is the tropical rainforest climate. It features a long annual wet season from March to October. The temperature at Jimma is in a comfortable range, with daily mean staying between 20°C and 25°C year-round.
For this study the researcher was used, worabe natural sand, manufactured sand, ordinary Portland cement, coarse aggregates from the local market, and water from Jimma Technology Institute Water Supply.
Since the research was an experimental study, the researcher was used different laboratory testing equipment. To mention some of them, sieves for both fine and coarse aggregates, enamel tree, oven, soaker, slump cone, cube mold, tamper, digital balance weight, compressive testing machine, flexural testing machine, ruler, test tubes, curing tank, and a plastic jar.
Sample size and sampling procedure
In this study, the purposive sampling technique was used for sampling. To determine the sample size of the test samples, it needs to consider the Standards’ specifications. According to ASTM 33; it requires a minimum of 3 samples of cube size of (150 × 150 × 150 mm) mold for each test of the characteristic compressive strength of concrete and (100 × 100 × 500 mm) for flexural strength. Total sample sizes of 72 samples were cast and tested at the age of 7th, 14th, & 28th days. These samples were used to conduct compressive and flexural strength.
C-25 concrete properties with partial replacement of river sand by manufactured sand.
• Percentage of manufactured sand.
• Properties of fine and coarse aggregates.
• Curing age of cubes.
The study was an experimental study of C-25 concrete properties with and without replacement of manufactured sand. The study was conducted in different steps. These include material preparation, determining engineering property of materials, and concrete compressive, and flexural strength tests.
All the laboratory investigations on the aggregates and concretes are carried out at Jimma University, Jimma Institute of Technology, Material Laboratory. Generally, natural sand and manufactured sand, ordinary Portland cement, coarse aggregates, and water were materials used in this study. This replacement material (manufactured sand) was taken from the aggregate crushing plant of the Jimma zone.
Sources of materials
a) Cement- Dangote OPC is available at markets. The product of this factory cement was purchased from the shops available at Jimma town.
b) Coarse aggregate, Natural Sand, and Manufactured sand - local market
c) Water -In this research, water is obtained from the Jimma Institute of technology water supply
Determining engineering property of materials by different methods
The engineering property of all materials necessary for describing the type of materials used and also properties that can affect the production of concrete were determined before production. The test methods used for the aggregates are listed in Table 1.
|Property tests||Test methods|
|A sieve analysis( natural river sand, manufactured sand, coarse ) aggregates||ASTM C136|
|Unit weight aggregates||ASTM C29|
|Silt content natural river sand||ASTM C117|
|Specific gravity and absorption aggregates||ASTM C127, BS 812:part 2:1995|
|Moisture content aggregates||ASTM C 566|
Sieve analysis and fineness modules
This is a procedure for the determination of the particle size distribution of the aggregate. It is also used to determine the fineness modulus, an index to the fineness, coarseness, and uniformity of aggregates. These properties of the aggregate greatly affect the property of the concrete. The sieve analysis both for fine and coarse aggregates were done by using standard square sieve openings.
Unit weight can be defined as the weight of a given volume of graded aggregate. It is thus a density measurement and is also known as bulk density. But this alternative term is similar to bulk specific gravity, which is quite a different quantity, and perhaps is not a good choice. The unit weight effectively measures the volume that the graded aggregate will occupy in concrete and includes both the solid aggregate particles and the voids between them. The unit weight is simply measured by filling a container of known volume and weighing it. However, the degree of compaction will change the amount of void space, and hence the value of the unit weight. Since the weight of the aggregate is dependent on the moisture content of the aggregate, the constant moisture content is required. An oven-dried aggregate sample is used in this test . The approximate bulk density (unit weight) of aggregate commonly used in normal-weight concrete ranges from about 1200 to 1750 kg/m3 (75 to 110 lb/ft3) .
Specific gravity and absorption capacity
Specific gravity is an expression of the density of an aggregate. It is the ratio between the weight of the substance and that of the same volume of water. Aggregates contain pores in their structure, therefore the specific gravity depends on whether the pores are included in the measurement or not. The apparent specific gravity of an aggregate refers to the solid materials excluding the pores and bulk specific gravity refers to total volume i.e. including pores of the aggregate.
The material in fine aggregates which is finer than 75μm is generally regarded as silt. This silt in the sand for the concrete has a severe effect on the quality of the concrete. It mainly affects the workability of the concrete, and also results in the reduction of strength.
Aggregates can hold water in two ways: absorbed within the aggregate porosity or held on the particle surface as a moisture film. Only the surface moisture, not the absorbed moisture, becomes part of the mixing water in concrete. Surface moisture percentages are used to calculate the amount of water in the aggregates to reduce the amount of mix water used for batching. Besides the batch weight of aggregates should be increased by the percentage of surface moisture present in each type of aggregate. If adjustments are not made during batching, surface water will replace a portion of the aggregate mass and the mix will not yield properly 
The absorption and surface moisture of aggregates should be determined so that the total water content of the concrete can be controlled and correct batch weights determined. The internal structure of an aggregate particle is made up of solid matter and voids that may or may not contain water . The moisture content of fine aggregates was determined by oven drying a sample of fine aggregate (500 g) in an oven at a temperature of 110°C for 24 hrs and dividing the weight difference by the oven-dry weight. Test for cement was not conducted because Dangotie (OPC) standard cement with a strength grade of 42.5 was used. The samples for the property test were taken from the production site by using the quartering method.
Concrete mix design
Mix design is the process of determining the required and specified characteristics of a concrete mixture. The required or specified concrete characteristics can be fresh concrete properties, mechanical properties of the hardened concrete such as strength and durability requirements, and the inclusion or exclusion of specific ingredients .
Concrete fresh properties
Concrete remains in its fresh state from the time it is mixed until it sets. During this time the concrete is handled, transported, placed, and compacted. Properties of concrete in its fresh state are very important because it influences the quality of the hardened concrete. Some of the fresh properties of the concrete are consistency, workability, settlement & bleeding, plastic shrinkage, and loss of consistency. Among these properties, the workability of the concrete is dominantly quality checking property in the fieldwork.
The workability of a concrete mix is the relative ease with which concrete can be placed, compacted, and finished without separation or segregation of the individual materials. Workability is not the same thing as consistency. Mixes with the same consistency can have different workability, if they are made with different sizes of stone the smaller the stone the more workable the concrete. It is not possible to measure workability but the slump test, together with an assessment of properties like stone content, cohesiveness, and plasticity, gives a useful indication .
Compressive and flexural strength test
A compressive strength test was carried out on the samples prepared to compare the compressive strength of the concrete with and without manufactured sand. Compressive strength tests of 7th, 14th, and 28th days were conducted according to Ethiopian standard after immersed in water for 7, 14, and 28 days respectively. The flexural strength of the study was conducted after curing for 28 days.
Data collection process
Filed observation: The field observation was comprised of supervising quarry sites and aggregates production companies that are available in the study area. The observation helps to get information about the sources of laboratory input data that the researcher was used in the laboratory tests.
Laboratory test: This is how the researcher used to collect data from the results of experimental procedures at the laboratory and record them in the proper format. The data is served as input for the analysis of the suitability replacement of natural sand with manufactured sand.
Data processing and analysis
To come across the research objectives, this part was conducted in two steps: the first step was evaluating some engineering properties of natural and manufactured sands and coarse aggregates and then determining the compressive and flexural strength of hardened concretes.
Analyzing concrete strength
The compressive and flexural strength of concrete both without and with manufactured sand was conducted by taking the mean of three samples as stated in the procedure of the Ethiopian standard (ES C.D4.001). The mean compressive strengths of concrete without manufactured sand were compared with each concrete cube samples with manufactured sand. Further, the data found were computed with different standards. According to ASTM(C 90- 70) and (ASTM C-129-70) average of three (3), concrete cube samples are required. Therefore, the means were computed and compared according to Ethiopian standards (ES. C.D3.301), and individually with ASTM the results were analyzed and presented in tables and graphs.
The use of manufactured sand as natural sand replacing material in concrete production was studied and after the research work is done, the following conclusions were made: Generally, as the replacing materials increase the absorption of the sample increase, specific unit weight decreases, specific gravity decreases, and the workability of fresh concrete decreases. The maximum compressive strength of natural sand replacement with manufactured sand was obtained at 40% replacement and the corresponding compressive strength is 31.25 MPa. The use of manufactured sand in the construction industry can save the environment and provide optimum exploitation of the resources. Generally, it is concluded, physical properties of fully or partially replaced natural sand by manufactured sand are fulfilled the minimum standards for unit weight, absorption, specific gravity, fineness modulus, and gradation at 40%. The workability of fresh concrete was decreased by 33.43% when manufactured sand increases from 10% to 60%. The maximum compressive and flexural strengths at 40% replacement were 31.25 MPa and 4.37 MPa respectively for the target concrete grade C-25 .
According to the study conducted on the suitability of natural sand replacement with manufactured sand for C-25 concrete properties with fully or partially replaced natural sand by manufactured sand the following recommendations are forwarded:
The construction units of the town administration should create awareness for the construction parties about the use of manufactured sand as partial replacements of natural sand to prevent unnecessary damages to the environment and provide optimum exploitation of the resources without compromising the strength of concrete.
The future researchers are recommended to conduct further studies on fine aggregate (manufactured sand) as partially replacing natural sand materials for concrete production, the different percentage that is not considered in this study.