Concrete Mix Design Testing - Lab Report Example

SCHOOL OF ENGINEERING - ENGINEERING MATERIALS AND CONSTRUCTION RUNNING HEAD: PBL 1 Project (Concrete Technology) Lab Section: Subject: Engineering Materials Lab Number: Lab Instructor: Date of Experiment: Date Due: Date Submitted: Group Members: Abstract Previous to this experimental tests, the group had designed a concrete mix, batched according to the mix ratios designed, and casted some test specimens. The concrete specimens involved 3 cylinders and one beam which were meant to be used in some destructive testing to verify certain strength parameters attributed to the designed concrete. The specimens were tested in a Young’s loading machine and flexural deflection tester. These measurements assisted in the determination of the actual concrete designed. The values were however, less than the expected and various reasons were attributes to that. Contents Abstract 2 Contents 3 List of Figures 5 Fig1. Cylinder Crushing Machine………………………………………7 5 Introduction 6 Description of Apparatus used for Testing 8 Fig1. Cylinder Crushing Machine 8 Aim 9 Procedure 9 Indirect Tensile Testing 11 Concrete mix design 12 Discussion 13 Results 13 15 Quality Control Plan and inspection during construction 17 References 18 Day, k (2000) Concrete Mix Design, Quality Control and Specification by 18 AS 3600: Australian Standards – Concrete Structures 18 AS 1012: Australian Standards - Testing of concrete 18 Ramachandran, V.S (2003) Concrete Admixtures Handbook, 2nd Ed. : Properties, Science and Technology 18 Appendix A 19 List of Figures Fig1. Cylinder Crushing Machine………………………………………7 Fig 2: Flexural Testing Machine ………………………………………….. 8 Figure 3- Concrete Compression testing, before………………………….….8 Figure 4- After Compression Testing………………………………………..9 Figure 1: Concrete cylinder split in half……………………………………..10 Figure 2- Testing Tensile Strength……………………………………………..11 Figure 3- Concrete Split………………………………………………………...11 Table 1: Concrete Cylinder B Results under Compression ……………………13 Fig 8: Designed Indirect Tensile strength:………………………………………14 Introduction Concrete refers to mixture of an inert material aggregate, sand, and a binding or cementing material. Usually this binding material is cement, although other binders such as gypsum or asphalt may be used, in this case the resulting concrete is known as gypsum concrete or asphalt concrete respectively. Characteristic and properties of concrete is dictated by either the respective properties of the ingredient materials (sand, course aggregate, water, and cement), and to a greater extent, by the relative ratios and proportions of these ingredients as used in the concrete mixing. It is advisable to select the proportions and ratios methodically so as to come up with concrete material with desired properties such as strength, durability, workability and of course economy (Ramachandran, 2003). The most common aggregate material used in mixing concrete is crushed sand and gravel. However, blast furnace slug, cinders, crushed brick, and other materials may be used depending on cost, availability, and desired final concrete characteristics as mentioned above. Usually aggregate material that is retained on a 0.187- inch sieve is arbitrarily referred to as course aggregate while the material that is retained is known as fine aggregate. Aggregate material with almost equal sized particles or with a lot fine particles, often required a lot of cement to effectively bind together the particles. Therefore an economical mixture should include varying particle sized of aggregate. Usually the best concrete should have adequate strength, at desirable workability at minimal cost. Strength as applied to concrete refers to the ultimate compressive strength exhibited by moist cured concrete at 28 day age. Most concrete material are often batched to give ultimate compressive strength of between 17MPa and 28MPa after 28 days. The modulus of elasticity of a concrete block is often approximately 1000 times its strength i.e. its ultimate compressive strength (Day, 2000). The ultimate compressive strength depends on the cement water ratio used in batching. Strong concrete is often associated with low water to cement ratio. Although the chemical reaction of setting of concrete requires less water; a lot more is often used to boost the workability of the concrete material. The objective of this experiment was to perform destructive testing on the casted concrete cylinders and prism. The tests performed are expected to yield expected results as per the specific mix design. The tests will include compressive tests, flexural deflection. The cylinders were dried wet for 28 days, then dried at room temperature at indoors and then dried outdoors while sheltered from the adverse weather elements. Portland cement is the commonly used cement around the world. The name is derived from the Isle of Portland in England where Joseph Aspin an Engineer patented the cement product in 1824. As a paste, Portland cement binds the loose aggregates together to form concrete mixture. In some instance accelerators such as admixtures are used to hasten the hydration process or retarders to slow down the same process for optimum concrete results. Certain desired results son strength and workability of concrete can be achieved when air entrainers, super plasticizers, plasticizers, and pigments are incorporated in the batching process (Day, 2000). In all this instances, curing at the right optimum conditions is essential in attaining the desired concrete attributes. Ideal curing occurs when concrete remains hydrated until the hydration process is complete. Effective hydration reduces the permeability of concrete and thus, increasing the ultimate concrete strength. Poor hydration leads to development of internal stresses responsible for cracking of exterior layers. This is because the inner portions are undergoing hydration while the outer layers are just dry. Typically concrete usually possesses tensile strength equivalent to a tenth of its ultimate compressive strength. To prevent such tensile cracking, reinforcement bars to aid in improving the tensile of concrete, also fibers can be equally added. Soft aggregate also lowers the strength of concrete, as case that happens if a cylinder is split in the middle. Description of Apparatus used for Testing Fig1. Cylinder Crushing Machine This machinev was used for gradual loading to determine the ultimate compressive strength of cylinders. For each of the test time, the cylinders were loaded onj the test appratus, and the load was gradually actuate at a controlled rate. Once the cylinder specimen attained its critical compressive load, on of the loading machine indicator recorded the exact failure point load. Fig 2: Flexural Testing Machine Flexural testing machine is used for measuring the strength and deformation properties of concrete materials. This test is particulary useful in ths application since concrete is oftenly used in form of beams where resistance to bending and deflection is a vitail parameter. Aim The concrete specimens involved 3 cylinders and one beam which were meant to be used in some destructive testing to verify certain strength parameters attributed to the designed concrete. The specimens were tested in a Young’s loading machine and flexural deflection tester. Procedure The concrete test cylinders and beam were taken from their curing location at the 28th day for testing. Each of the cylinders crossectional dimeter and lengths were measured with a dial caliper and tape measure. The average measurement waas recorded and used in later calculations. All this time the specimens were dipped in a water bath until the tests were done. Two cylinder specimens A&B were then tested in the youngs modulus machine. On the loading machine, the operator exerted gradual loading against the test piece until failure occurred. At the failure point load, the Young’s machine indicator pointer shows the failure load. The maximum compressive load was tested in the similar way as shown in the figure above. Figure 3- Concrete Compression testing, before. Figure 4- After Compression Testing The results were recorded as shown in the table shown in the results section The reinforced concrete beam was placed horizontally acorss the Flexural Testing Machine in order to test the beam maximum tensile stress. The load arm was placed haon the beam to produce point loading at the mid section of the beam length. In the above tests, the concrete beam broke into two pieces at the loading point. Unlike the commpressive loading tests donme earlier, the results were plotted on a stree/ strain through the displace over length. The displacement of concrete increased before ultimately failing by breaking. However the load remained the same and thus the modulus of elasticity is eqyuivalent to the slope of the stress/ strain graph. The maximum force require to cause the beam’s failure was measured and recorded. The testoing machine after testing was as shown in figure below. . Figure 4: Concrete cylinder split in half Indirect Tensile Testing This type of concrete tensile testing seeks to establish the concretes ability to withstand cracking and hence its durability. This type of tensile compressive testing is more dsignificant especially where the concrete is subjected to moist conditions as as this case where the concrete is meant to be used for making bridge abutments across the flow of water. Firstly, this concrete cylinder was arranged horizontally acrossthe machine loading bed. The machine was then gradually loaded until the cylinder split as a resulty of the tensile strength subjected. This method enabled the determination of the indirect tensile strength which was noted and recorded to be used later for calculation in discussion. Figure 5- Testing Tensile Strength Figure 6- Concrete Split Concrete mix design Concrete mixtures often given as volume ratios of sand gravel and sand were worked out. Calculation of mixing ratios expected to give the design ultimate compressive strength of 40Mpa were done as shown in Appendix A Finally the volumes ration arrived at were as follows; Water = 2.835 kg, Cement =6.03kg, Sand= 9.63kg, fine aggregate of 7mm sized- particles= 7.22 kg, and course aggregate of14mm particle size= 7.22 kg. This was the enough to batch for 3 cylinders and 2 prisms with additional margin of 15 percent. Discussion Results The results both in tabulated and graphical form as follows; Compression Cylinder Testing Compression Test Results Specimen Force (kN) A 216 B 208 Table 2: Concrete Cylinder A Compressive Test results Deflection versus Load Table 3: Concrete Cylinder B Results under Compression Deflection versus Load Fig: 7: Flexural Tensile Testing Results The maximum force recorded in the deflection test of the reinforced concrete beam was 216.79KN Flexural Test Results Specimen Force (kN) A 0.7194 B 0.884 Fig 8: Designed Indirect Tensile strength: Flexural Test Results Specimen Force (kN) A 1.48 The expected ultimate strength is 40Mpa; this comes to 32.25Mpa after factoring 75 percent strength. From the mathematical working provided in Appendix A, we get the expected failure load to be 255.25KN. The results shown in table above; obtained from the test therefore less than this expected figure. This negative result can be attributed to several valid reasons. First the air content and slump measurement for both were lower that the designed and expected figure. There are possibilities of errors arising from these low readings. One, when water was being filled in the bucket in order to use in the concrete mix, this may have contributed to reduced air content. Secondly, it’s worth noting that lower than expected and designed slump readings were recorded. The reduced batching water may have affected the cement: water ratio, thus affecting the percentage saturation of the fine aggregate and hence low compressive recorded. The lower slump may have been also as a result of poor air-entrainment in the concrete mixture. According to (Ramachandran, (2003), for every 2 percent drop or rise in entrained air content, there is a 25mm change in slump. The maximum force attained as a result of flexural tensile testing was 216Kn still less than the expected figure of 255 KN. This can be attributed to presence of large quantities of fine aggregate of not more than 7mm. this soft aggregate may lower the strength of concrete. This can be proved by the fact that after splitting in the middle, all the aggregates at this point of failure are intact. It is more likely that the failure occurred in the cement paste that is binding the aggregates together. It is also worth noting that another set of testing machines should have been used in order to check any errors that could be inherent in one set of machines. Quality Control Plan and inspection during construction To guarantee quality of concrete used in a project, certain important points should be adhered to. Before batching, through sampling and grading should be done in order to ascertain the average aggregate size. Sand used in based should be clean and free from any foreign material such as silt and organic matter which could inhibit proper mixing. Formwork material where used should not inhibit the hydration process of concrete, it should be water tight and should not hinder the curing process. Where reinforcement bars are used, proper inspection should be done to ensure even reinforcement as per design is achieved thus avoid excessive stresses in some reinforced regions than others. The reinforcement bars also should conform with the defined standards or the equivalent. Accelerators such as admixtures are used to speed up the hydration process or as retarders to slow down the same process for optimum concrete results. Certain desired results on strength and workability of concrete can be achieved when air entrainers, super plasticizers, plasticizers, and pigments are incorporated in the batching process. References Day, k (2000) Concrete Mix Design, Quality Control and Specification by AS 3600: Australian Standards – Concrete Structures AS 1012: Australian Standards - Testing of concrete Ramachandran, V.S (2003) Concrete Admixtures Handbook, 2nd Ed. : Properties, Science and Technology Appendix A Estimated compressive strength (KN): F = x A   F= predicted load A= cross-sectional area F =  F =  F = F Concrete Mix Design f’c = 40mPa min f’c for BI environnent = 32mPa Using the highest mPa fcm = f’c + ks Assume k = 1.65 s = 5.9 fcm = 40 + 1.65x5.9 fcm = 49.735 Therefore minimum slump is 50mm Assume the aggregate is crushed Using 50% 7mm aggregate and 50% 14mm aggregate 210kg water/m³ Assume type A cement 45mPa at 0.5 water/cement ration Therefore the water cement ration for 50mPa concrete is 0.47 Specific Gravity of aggregate 40% fine aggregate (sand) 60% coarse aggregate (crushed rock) SPG = 2.76 Wet Concrete Density = 2440kg/m³ Total Aggregate Content Cement Load TAC =2440 - (210+446.8) TAC =1783.2kg/m³ 40% sand = 713.28 kg/m³ 60% crushed rock = 1069.92 kg/m³ The 60% total aggregate is divided 50/50 into 7mm and 14mm 534.96 kg/m³ of 7mm aggregate 534.96 kg/m³ of 14mm aggregate TOTAL VOLUMETRIC QUANTITIES Water = 210 kg/m³ Cement = 446.8 kg/m³ Sand = 713.28 kg/m³ 7mm Agg = 534.96 kg/m³ 14mm Agg = 534.96 kg/m³ Cylinder Volume Prism Volume Total Quantity Required = 3 cylinders + 2 Prism + 15% TOTAL QUANTITY REQUIRED Water = 2.835 kg Cement = 6.03 kg Sand = 9.63 kg 7mm Agg = 7.22 kg 14mm Agg = 7.22 kg Read More

The ultimate compressive strength depends on the cement water ratio used in batching. Strong concrete is often associated with low water to cement ratio. Although the chemical reaction of setting of concrete requires less water; a lot more is often used to boost the workability of the concrete material. The objective of this experiment was to perform destructive testing on the casted concrete cylinders and prism. The tests performed are expected to yield expected results as per the specific mix design.

The tests will include compressive tests, flexural deflection. The cylinders were dried wet for 28 days, then dried at room temperature at indoors and then dried outdoors while sheltered from the adverse weather elements. Portland cement is the commonly used cement around the world. The name is derived from the Isle of Portland in England where Joseph Aspin an Engineer patented the cement product in 1824. As a paste, Portland cement binds the loose aggregates together to form concrete mixture.

In some instance accelerators such as admixtures are used to hasten the hydration process or retarders to slow down the same process for optimum concrete results. Certain desired results son strength and workability of concrete can be achieved when air entrainers, super plasticizers, plasticizers, and pigments are incorporated in the batching process (Day, 2000). In all this instances, curing at the right optimum conditions is essential in attaining the desired concrete attributes. Ideal curing occurs when concrete remains hydrated until the hydration process is complete.

Effective hydration reduces the permeability of concrete and thus, increasing the ultimate concrete strength. Poor hydration leads to development of internal stresses responsible for cracking of exterior layers. This is because the inner portions are undergoing hydration while the outer layers are just dry. Typically concrete usually possesses tensile strength equivalent to a tenth of its ultimate compressive strength. To prevent such tensile cracking, reinforcement bars to aid in improving the tensile of concrete, also fibers can be equally added.

Soft aggregate also lowers the strength of concrete, as case that happens if a cylinder is split in the middle. Description of Apparatus used for Testing Fig1. Cylinder Crushing Machine This machinev was used for gradual loading to determine the ultimate compressive strength of cylinders. For each of the test time, the cylinders were loaded onj the test appratus, and the load was gradually actuate at a controlled rate. Once the cylinder specimen attained its critical compressive load, on of the loading machine indicator recorded the exact failure point load.

Fig 2: Flexural Testing Machine Flexural testing machine is used for measuring the strength and deformation properties of concrete materials. This test is particulary useful in ths application since concrete is oftenly used in form of beams where resistance to bending and deflection is a vitail parameter. Aim The concrete specimens involved 3 cylinders and one beam which were meant to be used in some destructive testing to verify certain strength parameters attributed to the designed concrete.

The specimens were tested in a Young’s loading machine and flexural deflection tester. Procedure The concrete test cylinders and beam were taken from their curing location at the 28th day for testing. Each of the cylinders crossectional dimeter and lengths were measured with a dial caliper and tape measure. The average measurement waas recorded and used in later calculations. All this time the specimens were dipped in a water bath until the tests were done. Two cylinder specimens A&B were then tested in the youngs modulus machine.

On the loading machine, the operator exerted gradual loading against the test piece until failure occurred. At the failure point load, the Young’s machine indicator pointer shows the failure load. The maximum compressive load was tested in the similar way as shown in the figure above.

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