CIVE 2700: Civil Engineering Materials Fall Lab 2: Concrete. Ayebabomo Dambo

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1 CIVE 2700: Civil Engineering Materials Fall 2017 Lab 2: Concrete Ayebabomo Dambo Lab Date: 7th November, 2017 CARLETON UNIVERSITY

2 ABSTRACT Concrete is a versatile construction material used in bridges, houses, commercial buildings, etc. Megastructures like the Burj Khalifa and the Petronas Twin Towers were designed using concrete. It has a high compressive strength thus, it can withstand heavy weights on it. However, its characteristic low tensile strength will cause it to crack easily under tension. This laboratory experiment consisted of three sessions: (1) mix design of concrete; (2) casting of concrete and; (3) testing of concrete in tension and compression. Various components were used in producing 3 concrete cylinders with a diameter of 100mm and a height of 200mm while targeting a slump of 75mm and strength of 40 MPa - 45 MPa. After 28 days of curing, the cylinders underwent tension and compression tests. The compression test was carried out on two cylinders and the tension test was carried out on two other cylinders. A fifth cylinder wrapped In FRP (Fibre Reinforced Polymers) was also tested in compression to illustrate confinement. The cylinders placed under compression had cracks parallel to the direction of the applied load, which resulted in a cone-shaped failure while the cylinder placed under tension cracked down the middle into two symmetrical pieces. With the data from the compressometer which was attached to the cylinders under compression, a stress-strain curve will be plotted and comparisons between the failure types will be discussed in this report. i

3 TABLE OF CONTENTS OBJECTIVES...1 THEOERETICAL BACKGROUND...1 MATERIALS AND EQUIPMENT...4 EXPERIMENTAL PROCEDURE...5 ANALYSIS OF DATA...6 DISCUSSION OF RESULTS...9 CONCLUSION...10 REFERENCES...11 APPENDIX A: SAMPLE CALCULATIONS...12 APPENDIX B: RAW DATA...14 ii

4 LIST OF TABLES Table 1. Compressive Test Strength Results...7 Table 2. Given Specifications for Mix Design...12 Table 3. Raw Data for Compression Test Table 4. Raw Data for Compression Test Table 5. Raw Data for Tension Test Table 6. Raw Data for Tension Test Table 7. Raw Data for FRP-wrapped cylinder in compression...23 iii

5 LIST OF FIGURES Figure 1. Image showing the slump of concrete...1 Figure 2. Different types of slump...2 Figure 3. Coarse Aggregate (gravel (3/4 s crushed)...4 Figure 4. Fine Aggregate (Sand)...4 Figure 5. GUL (General Use Portland-Limestone) Cement...4 Figure 6. Water...4 Figure 7. Steps to measure the slump of the concrete...5 Figure 8. Graph of Strain vs Stress for first Compression Test...6 Figure 9. Graph of Stress vs Strain for Second Compression Test...7 Figure 10. Failure Pattern for Compressive Strength Test...8 Figure 11. Failure Pattern for FRP-wrapped Cylinder in Compression Test...8 Figure 12. Failure Pattern for Split Tensile Strength Test...8 iv

6 OBJECTIVES The objective of this lab is to understand the compressive and tensile properties of hardened concrete after 28 days of curing, and to note their failures and differences. This experiment is also carried out to enable students to understand how the modes of failure in concrete and steel under compression and tension differ as this knowledge is vital to the design of structures. THEORETICAL BACKGROUND Concrete is a composite building material made up of cement, water, fine aggregates (sand, etc.) and coarse aggregates (gravel, etc.). Depending on the purpose, the constituents of concrete are mixed in different proportions. This process is known as Concrete Mix Design. The volumetric mix design method prescribed by the American Concrete Institute s (ACI) Committee 211 was used for this lab. Concrete gains almost 80% of its ultimate strength 28 days after the mixing. The strength of the concrete is inversely proportional to the water-cement ratio (w/c). Thus, the lower the w/c, the higher the concrete strength. Air content also affects the strength of concrete. High levels of air will reduce the concrete strength. Other factors which affect the strength of the concrete are type of cement used, type of aggregates used and gradation of aggregates [1]. The volumetric mix design method requires the slump, strength, water and air requirements as well as the aggregate proportions to be determined. The required slump and strength for a given job is usually given with allowable tolerances. If this is not the case, Table 12-6 and Table 12-1 in the CAC Design Handbook can be used to determine the slump and strength respectively. Calculations for the mix design can be seen in Appendix A of this report. The slump test is carried out on fresh concrete to determine its workability, which is the ease of placing, consolidating, and finishing freshly mixed concrete. This test requires filling a truncated cone with concrete, removing the cone and measuring the distance the concrete slumps (see Figure 1) according to ASTM (American Standard for Testing Materials) C143 [2]. Figure 1. Image showing the slump of concrete [4] The results of the slump test indicate the water-cement ratio of the concrete: 1

7 Figure 2. Different types of slump [3] Zero slump shows that the workability is very low, collapsed slump shows that the workability is too high and shear slump indicates that concrete needs to be retested as the results are incomplete. A true slump is the only measurable slump in the test [3]. The water and air content in concrete and its water-cement ratio can also be estimated using information from the CAC Design Handbook while the gradation of the aggregates can be estimated knowing that: NMAS 15 Narrowest dimension of form or mold and for some constrictions, The cement weight is calculated using: NMAS 34 Clear space between reinforcement NMAS 13 Unreinforced slab on ground thickness where NMAS is the Nominal Maximum Aggregate Size (1) where Wcm is the weight of the cement Wwater is the weight of water added and w/c ratio is the water-cement ratio The coarse aggregate is estimated using: where WCoarseGravel is the oven-dry mass of coarse aggregate for one cubic-meter of concrete (2) 2

8 γcoarsegravel is the oven-dry bulk density of coarse aggregate and b is the bulk aggregate of coarse aggregate b 0 per unit volume of concrete The bulk aggregate is based on the NMAS and fineness moduli of the fine aggregate. The weight of the fine aggregate is then calculated thus: where V = Volume G = Specific Gravity γ = Density (3) This equation is used since fines occupy space not taken by the remaining materials. 3

9 MATERIALS AND EQUIPMENT The materials used for the following experiment are shown below: 1) 2) Fig. 3. Coarse Aggregate (gravel (3/4 s crushed)) Fig. 4. Fine Aggregate (sand) 3) 4) Fig. 5. GUL (General Use Portland-Limestone) Fig. 6. Water Cement 4

The equipment required for the completion of this experiment are listed below: Compressometer Universal loading machine Tamping rod Metre Rule Pan Mallet Trowel Hand scoop Shovel Wheelbarrow

10 The equipment required for the completion of this experiment are listed below: Compressometer Universal loading machine Tamping rod Metre Rule Pan Mallet Trowel Hand scoop Shovel Wheelbarrow Truncated Cone Cylinders Caps ( to distribute the load over the cylinder) EXPERIMENTAL PROCEDURE This laboratory experiment consisted of three sessions: (1) mix design of concrete; (2) casting of concrete and; (3) testing of concrete in tension and compression. For the mix design of concrete (ASTM C192), 2.5kg of water was mixed with the cement, sand and gravel (each having a mass of 6 kg) with 500g added at intervals. The mixture was done by hand for about 20 minutes using a shovel and wheelbarrow. After mixing the concrete, the slump test was then carried out. Slump Test Procedure (ASTM C143) : To carry out the slump test, the fresh concrete mix was poured into a truncated cone. The cone was then removed and the slump was measured using a tamping rod and a metre rule as shown in figure 7 below: Figure 7. Steps to measure the slump of the concrete [3] 5

11 Stress (KPa) After the slump test, the concrete mix was then cast into 4 cylinders using the hand scoop. This was kept for 28 days in a curing chamber where the humidity is controlled (ASTM C39). After 28 days of curing, the concrete cylinders were removed from their containers and tested in compression and tension Compression Test Procedure (ASTM C39): For the compression test, two concrete cylinders were placed vertically in the Universal Loading Machine with sulphur caps placed at each end of the cylinder to distribute the load coming from the Machine and a compressometer to measure the strain. Another concrete cylinder was wrapped in FRP and placed in the machine with two big plates at each end and with no displacement gauge. After failure, the concrete cylinders were then crushed to significantly see the failure shape. Tension Test Procedure (ASTM C39): Two concrete cylinders were tested in tension. Styrofoam strips were attached transversely on each cylinder to prevent rolling/slipping in the machine. The cylinders were then placed separately, in a horizontal manner, into the Universal Loading Machine until failure occurred. ANALYSIS OF DATA Strain - Stress Curve for First Compression Test y= 2E+07x E = 20MPa Strain (mm/mm) Figure 8. Graph of Strain vs Stress for first Compression Test At the first compressive test, the concrete failed at the stress of 48.1 MPa. 6

12 Stress (KPa) Strain-Stress Curve for Second Compression Test y= 2E + 07x E = 20MPa Strain (mm/mm) Figure 9. Graph of Stress vs Strain for Second Compression Test At the second compressive test, the concrete failed at stress 47.6 MPa. Concrete 1 Concrete MPa 47.16MPa Table 1. Compressive Test Strength Results 7

Observed Failure Patterns: Fig. 10. Failure Pattern for Compressive Strength Test Fig.

12 Failure Pattern for Split Tensile Strength Test Strain gauge malfunctioned during split tensile strength.

However, from given data in Appendix B, the failure stress during the first tension test was 14.

13 Observed Failure Patterns: Fig. 10. Failure Pattern for Compressive Strength Test Fig. 11 Failure Pattern for FRPwrapped Cylinder in Compression Test Fig. 12 Failure Pattern for Split Tensile Strength Test Strain gauge malfunctioned during split tensile strength. As a result, a credible plot showing the stress-strain relationship could not be done. However, from given data in Appendix B, the failure stress during the first tension test was 14.5 MPa and that of the second tension test was 11.6 MPa. The failure stress for the concrete wrapped in FRP is 52.9MPa. This value was obtained from the data in Appendix B. A stress-strain curve could not be plotted as no displacement gauge was attached to the concrete. 8

14 DISCUSSION OF RESULTS The typical design values for the strength of the concrete and the slump are 40 MPa and 75mm respectively. A slump of 160mm was measured for this experiment. This slump was a collapse slump indicating a high workability. Compressive strengths of 48.1 MPa and 47.6 MPa were observed during the two compression tests. These strengths differ moderately from the typical value of 40MPa. The typical tensile strength of concrete is 2-5 MPa, but in this experiment the observed tensile strength was MPa, and MPa which fall completely outside of the expected values. This might be a result of the wires on the testing mechanism breaking before the tensile tests were done. The observed compressive strength was much higher than the tensile strength of the concrete. This is typical of concrete as this material is known to have a good compressive strength but weak tensile strength. In lab 1 the compressive strength of two steel members of varying lengths were tested. The steel members exhibited local and euler buckling respectively whereas concrete exhibited a brittle fracture. After the compression test, the concrete sheared in a cone-shaped structure while the concrete in tension cracked down its centre, causing it to split into equal halves. The difference in the failure mode of each of concrete and steel is as a result of the nature of each material. Steel is a very ductile material and as a result will stretch, or contract due to the external forces, whereas concrete is not a brittle material and instead shatters if the external force acting is great enough. The failure pattern of the concrete varied depending on the type of strength test it was exposed to. For the compressive test the failure pattern was shear-conic as shown in figures 10 and 11. This failure pattern is close to the expected fail pattern from this experiment. This failure pattern indicates that the test was done correctly under standardized testing procedures, other fail patterns such as shear or column indicate that either the concrete was mixed improperly or that the testing procedure was not followed correctly [5]. The failure pattern in the tensile test was down the middle, splitting the cylinder in half as shown in figure 12. This failure pattern is also typical of a splitting tensile strength test, as the force is applied directly along the vertical plane, a different failure pattern would indicate either an improper mix or the testing procedures not being correctly followed. There exists several possible sources of error in this experiment. Although this lab required adherence to the ASTM C143 standard for slump test, all procedures were not accurately followed. The measured slump was a source of error in this lab because it was a collapse slump. This was probably because the water content adjustment due to the natural moisture in the aggregates were not performed. According to the ASTM C143 standard, two slump tests are to be carried out to obtain accuracy [6]. This was not done and the value of the collapse slump was used for the experiment, thereby affecting results. Another source of error is the wire breakage that occurred while tests were being carried out. Lastly, an error could come from the curing chamber where the concrete cylinders were held to allow the hydration reaction to occur, if the humidity were to have not been held constant at all times throughout the curing process the strength of the concrete could be affected. Due to the presence of all these errors, the concrete produced did not meet the desired concrete characteristics for the mix design. 9

15 CONCLUSION Through the completion of this experiment a better understanding of concrete as a civil engineering material was established. Through the process of determining the mix design of the concrete a better knowledge of the process engineers would go through in the field was obtained. Testing the compressive and tensile strength of the concrete cylinders aided in comprehending the mechanical properties of concrete and their limitations in real world applications. 10

16 REFERENCES [1] Gales, J. (2017). Civil Engineering Materials Lab 2: Concrete Manual [docx]. [2] Mamlouk, M. S., & Zaniewski, J. P. (n.d.). Materials for Civil and Construction Engineers (3rd ed.). Prentice Hall. [3] Concrete Slump Test for Workability -Procedure and Results. (n.d.). Retrieved November 13, 2017, from [4] ACI Mix Design [pdf]. (n.d.). [5] BEZERRA, U. T., ALVES, S. M., BARBOSA, N. P., & TORRES, S. M. (n.d.). Hourglassshaped specimen: compressive strength of concrete and mortar (numerical and experimental analyses). Retrieved November 17, 2017, from [6] Standard Test Method for Slump of Hydraulic-Cement Concrete. (n.d.). Retrieved November 14,

17 MIX DESIGN CALCULATIONS APPENDIX A: SAMPLE CALCULATIONS Coarse Aggregate Fine Aggregate Cement Type Maximum Aggregate Size = Specific Gravity = Type = 10 / GUL 9.5mm Specific Gravity = Fine Modulus = 2.98 Specific Gravity = 3.14 Density = 1600 kg/m3 Table 2. Given Specifications for Mix Design Slump = 75 mm NMAS = 9.5mm For Water and Air content (Assuming non-air entrained) According to Table 12-1 from the CAC Design Handbook, Water = 228kg, Air = 3% To find required strength, f c = 40MPa + 10MPa = 50MPa (since exposure conditions do not govern this situation) To determine w/c ratio By interpolating data from Table 12-3 in the CAC Design Handbook, ( w c ) = w c = 0.34 To calculate cement weight using (1): W cem = W water w/c W cem = 228kg/m = kg To estimate weight of coarse aggregate using (2): Based on the Fine Modulus = 2.98 and NMAS 10mm, the bulk aggregate b b 0 can be interpolated using Table 12-4 in the CAC Design Handbook = b b 0 b = b 0 12

18 W CA = kg = kg To estimate weight of fine aggregate using (3): V sand = V T (V cem + V CA + V W V air ) = 1m kg kg 228 kg 3 ( + + ) 1000kg m 3 = m 3 W sand = V sand SG sand γ w = m kg m 3 W sand = 693 kg/m 3 m 3 13

19 Table 3. Raw Data for Compression Test 1 Load (kn) Platen Stroke(mm) APPENDIX B: RAW DATA Compressometer deformation (mm) Temperature Strain(mm/mm) Stress (KPa)

21 Table 4. Raw Data for Compression Test 2 Load (kn) Platen Stroke Compressometer Deformation (mm) Temperature ( C) Strain (mm/mm) Stress (KPa) (mm) E

22 Table 5. Raw Data for Tension Test 1 Load (kn) Platen Stroke (mm) Compressometer Deformation (mm) Temperature ( C) Strain (mm/mm) Stress (KPa)

25 Table 6. Raw Data for Tension Test 2 Load (kn) Platen Stroke (mm) Compressometer deformation (mm) Temperature ( C) Stress (KPa) Strain (mm/mm)

28 Table 7. Raw Data for FRP-wrapped Concrete in Compression Load (kn) Platen Stroke (mm) Compression Deformation (mm) Temperature ( C)

Chapter. Materials. 1.1 Notations Used in This Chapter

Chapter. Materials. 1.1 Notations Used in This Chapter Chapter 1 Materials 1.1 Notations Used in This Chapter A Area of concrete cross-section C s Constant depending on the type of curing C t Creep coefficient (C t = ε sp /ε i ) C u Ultimate creep coefficient