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EGB270 Civil Engineering Materials Assessment Number 01 - 1.1 Concrete Mixing - 1.2 Test of concrete strength DECLARATION I am aware of the University rule that a student must not act in a manner which constitutes academic dishonesty as stated and explained in the QUT Manual of Policies and Procedures (Section C, Part 5.3 Academic Dishonesty , accessible via http://www.mopp.qut.edu.au/C/C_05_03.jsp ). I confirm that this work represents my individual effort and does not contain plagiarised material. Signature ______________________________________________________ Date : 2

Abstract The subject of this report if that of the most widely used material in civil and structural construction worldwide – concrete. The following report covers the design and mixing method of concrete and how this process takes place, including measurements, diagrams, photos, and how certain data was collected. Additionally, it will also comprise of a series of compressive strength tests on the concrete produced. The results of both the concrete design and mix along with the compressive tests will be analysed and the findings will be discussed through academic and definitive reasoning. Finally, a summary of everything found will be given and recommendations of how to better produce and/or test in future practicals of the same nature. The findings of the report are important as they illustrate the fundamental knowledge required to produce concrete and its behaviour, whether that be workability, durability, or strength.

List of Tables Figure 1: Drawing of the equipment used in practical one .......................................................................... 1 Figure 2: Slump from the Slump Cone test in Practical 1 ............................................................................. 3 Figure 3: Image of the Schmidt Hammer test being conducted on cylinder 3 ............................................. 5 Figure 4: Sample one of the compressive tests. Failed at 325.16 kilonewtons due to shear failure ............ 5 Figure 5: Sample one of the compressive tests. Failed at 325.16 kilonewtons due to shear failure ............ 5 Figure 6: Sample two of the compressive tests. Failed at 285.85 kilonewtons due to columnar failure ...... 6 Figure 7: Sample two of the compressive tests. Failed at 285.85 kilonewtons due to columnar failure ..... 6 Figure 8 Sample three of the compressive tests. Failed at 372.88 kilonewtons due to shear failure ........... 6 Figure 9: Sample three of the comprfessive tests. Failed at 372.88 kilonewtons due to shear failure ........ 6 List of Figures Table 1: Mix proportions; provided and calculated ...................................................................................... 4 Table 2: All data gained from compressive tests on the concrete columns .................................................. 8

EGB270 Civil Engineering Materials Assessment Number 01 1 Objectives Over the course of two practical sessions, a series of tests were conducted, all of which hold relevant information and data. In these practical sessions, a desired concrete design strength was chosen, produced, and tested weeks later. The objective of this report is to describe the processes of the labs, deliver the results collected from these practical sessions and link to relevant theory, provide detailed analysis and discussion of the results through comparison and reasoning, and finally present recommendations for future laboratory testings. 2 Materials and Equipment In these practicals, the following lists provide all the materials and equipment used for concrete mixing, the slump test, creating concrete moulds, and concrete testing. 2.1 Practical 1 - Concrete mixes o Gravel (coarse) – 4.66kg o Sand (fine) – 5.46kg o Water – 1.50kg o Cement – 3.38kg - Pan mixer - Scale (for finding weight) N10624121 1 Figure 1: Drawing of the equipment used in practical one.

EGB270 Civil Engineering Materials Assessment Number 01 then added to the slump cone, filling it one third of the way each time and using the tamping rod to prod the mixture 25 times. This was repeated each time until the slump cone was filled and levelled. Once ready, the slump cone was slowly removed, and the slump was measured using the slump cone which was turned upside down and measured from the top of the cone to the top of the concrete. The mixture from the slump cone test was placed back into the pan mixer and mixed for another ten minutes. Once this mixing process was complete, the concrete mixture was used to fill the concrete moulds, filling one third of the mould at a time and using the tamping rod to prod the concrete 25 times until all moulds are full. These moulds were then labelled and set aside for 35 days to set and cure, ready for testing in practical 2. 3.2 Practical 2 Procedure Following practical 1, the three concrete moulds produced 35 days prior were set and ready for testing. Before the cylinders could be tested, size measurements of all three cylinders were taken. These measurements included the diameter and height of each cylinder. Multiple measurements were taken for each cylinder and a mean was calculated accounting for irregularities across the three samples. The concrete columns were then put through two different testing methods, one destructive and one non- destructive. The non-destructive test was conducted first, where using a Schmidt hammer, compressing this device 9 times on the top of the columns in different locations each time, gave a hardness reading in Megapascals. Once complete, each column was individually placed into the compressive machine which would apply 20MPa per minute until the concrete mould would fail. The total amount of force required to break the concrete was recorded and the failure mode was determined. 4 Test Results 4.1 Practical 1 The slump test conducted in the first practical, found that the specific concrete mix provided (presented in Table 1 ) gave a slump of 190mm. While this is a very large slump reading, since the sample did not shear, there was no need to redo the test. N10624121 3 Figure 2: Slump from the Slump Cone test in Practical 1

EGB270 Civil Engineering Materials Assessment Number 01 Additionally, a large set of calculations were completed to find the mix proportions needed to make 40MPa concrete. These proportions slightly differ from the actual ingredients provided in the lab practical. Table 1: Mix proportions; provided and calculated. Mix Proportion Provided Mix Proportion Calculated Cement 3.38kg 3.26kg Water 1.50kg 1.37kg Coarse Aggregate 4.66kg 4.50kg Fine Aggregate 5.46kg 5.27kg The formulae for finding the mix proportions are as follows: x ( ¿¿ 2 − x 1 ) y = y 1 +( x − x 1 ) ( y 2 − y 1 ) ¿ ( 1.1 ) W cement = W water w / c ratio ( 1.2 ) ( W OD ) = Volume×dry rodded weight ( 1.3 ) W SSD =[ W OD ( 1 + AC ) ] ( 1.4 ) V fines = V conc − V water − V cement − V coarse − V air ( 1.5 ) V conc = 1 m 3 ( 1.6 ) V water = Weight of water Water density ( 1.7 ) V cement = Cement weight Cement density ( 1.8 ) V coarse = W SSD , CA CA Density ( 1.9 ) V air = % of air 100 ( 1.10 ) N10624121 4

EGB270 Civil Engineering Materials Assessment Number 01 Each concrete cylinder was placed into the compression machine which applied 20MPa per minute until the sample failed under the load. Each test gave a maximum load held by the cylinder in newtons, and clearly visible signs of failure. N10624121 6 Figure 4&5: Sample one of the compressive tests. Failed at 325.16 kilonewtons due to shear failure. Figure 4

EGB270 Civil Engineering Materials Assessment Number 01 Once the diameter, height, mass and maximum load held by the concrete samples had been gathered and calculated, the following equations were used to find the remaining values present in Table 2 . Compressive Strength ( f c ) = Ultimate Load ( P )( kN ) Cross Sectional Area ( A ) ( 2.2 ) Density ( ρ ) = Mass ( M ) Volume ( V ) ( 2.3 ) Standard Deviation ( S )= √ ∑ ( f c − f cm ) 2 n − 1 ( 2.4 ) Characteristic strength ( f ' c ) = f cm − kS ( 2.5 ) N10624121 7 Figure 6&7: Sample two of the compressive tests. Failed at 285.85 kilonewtons due to columnar failure. Figure 8&9 Sample three of the compressive tests. Failed at 372.88 kilonewtons due to shear failure. Figure 5

EGB270 Civil Engineering Materials Assessment Number 01 The first compressive tests conducted on the concrete were done with a Schmidt hammer, used to measure the surface hardness and penetration resistance of the concrete (Proceq, 2019). Readings on the hammer are in megapascals and should have given a near estimate of the maximum compressive strength of the concrete. This was not the case, with the three concrete samples tested, the values gathered ranged from only 6 to 10 MPa. The reason these results were so low is because of the roughness of the top of each cylinder. Since the top of each cylinder was rough and uneven, this meant the Schmidt hammer was able to break small pieces of concrete off after each compression, giving a reading of significantly low surface hardness, such the results gathered in these tests. For the compressive tests conducted using the compression machine, a wide range of values were gathered for the compressive strength of the concrete. While it was predicted during the first practical that the compressive strengths would be far less than the designed strength of the concrete, 40MPa, the average compressive strength of the samples was 40.812MPa, 0.812MPa higher then designed. It is probable that for the slump test, the concrete mixture had not been mixed enough, or rather, a lot of the excess water in the mixture left during the curing stage. While the average strength of the concrete across the three tests is near to the desired strength of 40MPa, the range and standard deviation of these results considerable. Cylinders 2 and 3 stand out when comparing the two. Cylinder 2 had a compressive strength of only 35.655Mpa whereas, cylinder 3 had a compressive strength of 46.911MPa, a very substantial difference of 11.256MPa. Due to these two extremely different results, the standard deviation of results is very high (5.687MPa). The large difference in compressive strengths of the two concrete samples – despite coming from the same batch of concrete mix – is likely attributable to the interfacial transition zone (ITZ) where failure in the column was observed. The microcracks that were formed in between the cement paste and coarse aggregate throughout curing due to thermal movement and shrinkage in the concrete are what make the interfacial transition zone in concrete (Nicolas, 2015). Controlling the ITZ in the given conditions was not possible, meaning the interfacial transition zones and bonds formed across the three samples were grossly different, resulting in substantial deviations during testing. 6 Conclusions and Recommendations Throughout this report, the most used structural material internationally, concrete, was assessed. This included the process for calculating the mix proportions for a desired strength concrete and how to correctly mix them which would produce a concrete paste. Additionally, three different ways of testing concrete were covered, including a slump test and two different ways of compressive testing, Schmidt hammer and by compression in a compressive machine. It was found that despite the significantly larger slump then designed for, this did not affect the strength of the concrete after curing. It was also found that the Schmidt hammer test is a defective way of attaining the ultimate compressive strength of a concrete, particularly when the concrete surface being tested is not smooth. It should also be noted that it was discovered, there are inconsistencies throughout concrete predominantly in the interfacial N10624121 9

EGB270 Civil Engineering Materials Assessment Number 01 transition zones, between the coarse aggregates and the cement paste, and there is little that can be done to strengthen these zones in certain conditions. It is recommended that if these practicals were to be repeated, more slump tests be conducted to gain a more accurate value by the means of taking an average for the entire concrete mixture, and more concrete cylinder samples be prepared, allowing for more compressive tests to be conducted, in particular, the compressive machine. N10624121 10

EGB270 Civil Engineering Materials Assessment Number 01 Appendices Appendix A Mix design/proportion Calculations: Parameters : Slump : 75-100mm Cement : General purpose cement, Specific Gravity = 3.15 Coarse Aggregate: Maximum Aggregate size = 12mm, Bulk Specific Gravity (SSD condition) = 2.65, Moisture content = -0.5% (Effective absorption), Absorption capacity = 1%, Dry rodded unit weight = 1500 kg / m 3 Sand: Fineness Modulus = 3.5, Bulk specific gravity (SSD condition) =2.65, Moisture content = -1% (effective absorption), Absorption capacity = 1.5% W/C ratio: 40Mpa Step 1) Select slump - 100mm Step 2) Max aggregate size - 12mm Step 3) Estimate Water and Air content x ( ¿¿ 2 − x 1 ) W water = y 1 +( x − x 1 ) ( y 2 − y 1 ) ¿ x ( ¿¿ 2 − x 1 ) Air content = y 1 +( x − x 1 ) ( y 2 − y 1 ) ¿ N10624121 12 Using interpolation find air content for 12mm agg size. 9.5mm = 3 and 12.5mm = 2.5 Using interpolation find water content for 12mm agg size. 9.5mm = 228 and 12.5mm = 216

EGB270 Civil Engineering Materials Assessment Number 01 W water = 228 +( 12 − 9.5 ) ( 216 − 228 ) ( 12.5 − 9.5 ) Air content = 3 +( 12 − 9.5 ) ( 2.5 − 3 ) ( 12.5 − 9.5 ) W water = 218 kg / m 3 Air content = 2.58% Step 4) select Water content ratio. For 40 Mpa non air entrained concrete W / Cratio = 0.42 Step 5) Calculate amount of cement W cement = W water w / c ratio W cement = 218 0.42 W cement = 519.048 kg / m 3 Step 6) Estimate coarse aggregate amount in SSD conditions Volume = 0.4 +( 12 − 9.5 ) ( 0.49 − 0.4 ) ( 12.5 − 9.5 ) Volume = 0.475 W OD = Volume×dry rodded untiweight W OD = 0.475 × 1500 W OD = 712.5 kg W SSD = [ W OD ( 1 + AC ) ] W SSD = [ 712.5 ( 1 + 0.01 ) ] W SSD = 719.625 kg / m 3 Step 7) Calculate amount of fine aggregate in SSD condition V fines = V conc − V water − V cement − V coarse − V air N10624121 13

EGB270 Civil Engineering Materials Assessment Number 01 W SSD , FA = W conc − W water − W cement − W SSD , CA W SSD , FA = 2305 − 218 − 519.048 − 719.625 W SSD, FA = 848.327 kg / m 3 Average weight of the fines fines = 845.880 + 848.327 2 fines = 847.104 kg / m 3 Step 8) Adjust for moisture content W stock = W SSD ( 1 − EA ) W stock coarse = 719.625 ( 1 − 0.005 ) W stock coarse = 716.027 kg / m 3 W stock fines = 847.104 ( 1 − 0.01 ) W stock fines = 838.633 kg / m 3 To find volume of each to use for practical, multiply volume of the three-cylinder moulds by the weights for each: 100 mmdiameter , 200 mmheight with 33% extra Volume = ( π r 2 ) ×h Volume = ( π × 0.05 2 ) × 0.2 Volume = 0.00157 + ( 0.00157 × 1 3 ) Volume = 0.00209 × 3 Volume = 0.00628 m 3 W cement = 519.048 × 0.00628 W cement = 3.26 kg W water = 218 × 0.00628 N10624121 15

EGB270 Civil Engineering Materials Assessment Number 01 W water = 1.37 kg W coarse = 716.027 × 0.00628 W coarse = 4.50 kg W fines = 838.633 × 0.00628 W fines = 5.27 kg So weget : Cement = 3.26 kg Water = 1.37 kg C oarse = 4.50 kg Fines = 5.27 kg Appendix B Cylinder 1 Calculations Compressive Strength ( f c ) = Ulitmate Load ( P )( kN ) Cross Sectional Area ( A ) f c = 325.16 ( π × 0.1019 2 4 ) f c = 39.871 MPa Density ( ρ ) = Mass ( M ) Volume ( V ) ρ = 3.859 ( π × 0.1019 2 4 ) × 0.207 ρ = 2285.947 kg / m 3 to nearest 5 kg / m 3 , ρ = 2285 kg / m 3 Cylinder 2 f c = 285.85 ( π × 0.101033 2 4 ) N10624121 16