3020 Lab 5

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Laboratory 5: Hardened Concrete Properties CEE 3020 Civil Engineering Materials Submitted to: Alexandra Wu by: Sachin Dasu Section B6 Group B Thomas Reid Cabe III Katerina Efthymiou Maggie Jiang Shruti Sarkar Sarah Elizabeth Scioli Abstract 10% Introduction 10% Experiment 5% Results 25% Discussion 25% Conclusion 10% Technical Writing 10% Graphics: Design 5% TOTAL Due Date: December 4, 2023

Abstract The objectives of this experiment are to perform compression and splitting tensile strength tests, to draw conclusions regarding the influence of mixture design (w/cm, materials used), and concrete age on compressive and splitting tensile strength, and to characterize concrete using microscopy. The average compressive strength and the average tensile strength of the concrete tested was found to be 4051 psi and 620 psi, respectively. The standard deviation of the compressive strength and tensile strength was found to be 425 psi, and 100 psi respectively. The overall semester data degrading fly ash concretes (both 20% and 40%) were used to compare with the type 1 concrete tested as well. Through this laboratory experiment, it is determined that generally, an increase in w/c ratio will decrease the compressive strength of a concrete, and that increasing the age of curing of a concrete will also increase the compressive strength of a concrete.

Table of Contents Introduction ...................................................................................................................................... 1 Experiment ....................................................................................................................................... 1 Materials ................................................................................................................................... 1 Equipment ................................................................................................................................ 1 Procedure .................................................................................................................................. 1 Results .............................................................................................................................................. 1 Discussion ........................................................................................................................................ 7 Conclusion ........................................................................................................................................ 9 References ...................................................................................................................................... 10 Appendices ..................................................................................................................................... 11

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1 Introduction The Hardened Concrete Properties lab aims to perform compression and splitting tensile strength tests, to draw conclusions regarding the influence of mixture design (w/cm, materials used), and concrete age on compressive and splitting tensile strength, and to characterize concrete using microscopy. The first part of the Hardened Concrete Properties laboratory aims to calculate the compressive strengths of the concrete specimens, and the second parts aims to calculate the tensile strengths of the concrete specimens. The average compressive and tensile strengths are found, as well as the standard deviation of both values as well. Experiment Materials The materials are as described in the laboratory handout (Dai, 2023a). Equipment The materials are as described in the laboratory handout (Dai, 2023a). Procedure The materials are as described in the laboratory handout (Dai, 2023a). Results 1. The compressive strength and the tensile strength of each of the cylinders tested is shown in the table below. The average compressive strength and average tensile strengths are also provided. The standard deviation of the compressive strength and the standard deviation of the tensile strength are also provided. Specimen Diameter (in) Length (in) Maximum Load (lbs) Compressive Strength (psi) Fracture Mode Tensile Strength (psi) % of Aggregate Fractured (estimated %) 1 3 - 28800 4074 Shear - - 2 3 - 23660 3347 Core & Shear - - 3 3 - 31800 4498 Shear - - 4 3 - 29540 4179 Columnar - - 5 3 - 29360 4153 Columnar - - Average Compressive Strength = 4051 psi Standard Deviation of Compressive Strength = 425 psi 6 3 6 20000 - - 707 70 7 3 5.94 17920 - - 641 50 8 3 6 14460 - - 511 50 Average Tensile Strength = 620 psi Standard Deviation of Tensile Strength = 100 psi Table 1. Compressive Strength and Tensile Strength Data and Results Sample calculations and formulas are provided below. Compressive Strength = 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 𝐶𝐶𝐶𝐶𝐿𝐿𝐶𝐶𝐶𝐶 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝐿𝐿𝑆𝑆𝐿𝐿𝑆𝑆 𝐴𝐴𝐶𝐶𝑆𝑆𝐿𝐿 = 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 � 𝜋𝜋 4 �∗ ( 𝐿𝐿 2 ) = 28800 𝑆𝑆𝑙𝑙𝐶𝐶 � 𝜋𝜋 4 �∗ ( 3 2 ) 𝑆𝑆𝑆𝑆 ^ 2 = 4074 𝑝𝑝𝑝𝑝𝑝𝑝

2 Tensile Strength = 2∗𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 𝜋𝜋∗𝐿𝐿∗𝐿𝐿 = 2∗20000 𝑆𝑆𝑙𝑙𝐶𝐶 𝜋𝜋∗ ( 3 𝑆𝑆𝑆𝑆 ) ∗ ( 6 𝑆𝑆𝑆𝑆 ) = 707 𝑝𝑝𝑝𝑝𝑝𝑝 Average Compressive Strength = ∑ 𝐶𝐶𝐿𝐿𝐶𝐶𝐶𝐶𝐶𝐶𝑆𝑆𝐶𝐶𝐶𝐶𝑆𝑆𝐶𝐶𝑆𝑆 𝑆𝑆𝑆𝑆𝐶𝐶𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆ℎ 𝑁𝑁𝑁𝑁𝐶𝐶𝑙𝑙𝑆𝑆𝐶𝐶 𝐿𝐿𝑜𝑜 𝐼𝐼𝑆𝑆𝐶𝐶𝑆𝑆𝐿𝐿𝑆𝑆𝑆𝑆𝑆𝑆𝐶𝐶 Average Tensile Strength = ∑ 𝑇𝑇𝑆𝑆𝑆𝑆𝐶𝐶𝑆𝑆𝑆𝑆𝑆𝑆 𝑆𝑆𝑆𝑆𝐶𝐶𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆ℎ 𝑁𝑁𝑁𝑁𝐶𝐶𝑙𝑙𝑆𝑆𝐶𝐶 𝐿𝐿𝑜𝑜 𝐼𝐼𝑆𝑆𝐶𝐶𝑆𝑆𝐿𝐿𝑆𝑆𝑆𝑆𝑆𝑆𝐶𝐶 Standard Deviation of Compressive Strength = √ ( ∑ ( 𝑥𝑥 𝑆𝑆 − 𝑥𝑥̅ )^2)) 𝑆𝑆 𝑆𝑆=1 / (n-1) Standard Deviation of Tensile Strength = √ ( ∑ ( 𝑥𝑥 𝑆𝑆 − 𝑥𝑥̅ )^2)) 𝑆𝑆 𝑆𝑆=1 / (n-1) 2. The table below provides photos of the failure modes in the compression test performed in this laboratory experiment. Two specimens had a shear fracture mode. One specimen had a core and shear fracture mode. Two specimens had a columnar fracture mode. Specimen Photo Fracture Mode 1 Shear 2 Core & Shear 3 Shear 4 Columnar

3 5 Columnar Table 2. Specimen Photos and Fracture Modes 3. i. The figure below contains data from all of the mixtures prepared this semester as a graph for the ordinary concrete and the two fly ash concretes (fog room cured) showing the compressive strength of concrete (y-axis) at 7 days of age with the w/c of the mixture (x- axis). Figure 1. Compressive Strength of 7 Days of Age ii. The figure below contains data from all of the mixtures prepared this semester as a graph for the ordinary concrete and the two fly ash concretes (fog room cured) showing the compressive strength of concrete (y-axis) at 14 days of age with the w/c of the mixture (x- axis). 500 1500 2500 3500 4500 5500 6500 0.4 0.45 0.5 0.55 0.6 0.65 Compressive Strength (psi) w/c ratio Type 1 20% 40%

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4 Figure 2. Compressive Strength of 14 Days of Age iii. a. The figure below contains data from all of the mixtures prepared this semester as a graph comparing the effect of cement type (ordinary Type I or cement/fly ash) on the compressive strength (y-axis) of fog cured concrete for each w/c at 7 days (the horizontal axis labels will be the four w/c ratios). Figure 3. Comparison of Cement Type on Compressive Strength at 7 Days of Age b. The figure below contains data from all of the mixtures prepared this semester as a graph comparing the effect of cement type (ordinary Type I or cement/fly ash) on the compressive strength (y-axis) of fog cured concrete for each w/c at 14 days (the horizontal axis labels will be the four w/c ratios). 1500 2000 2500 3000 3500 4000 4500 5000 5500 0.4 0.45 0.5 0.55 0.6 0.65 Compressive Strength (psi) w/c Ratio Type 1 20% 40% 0 1000 2000 3000 4000 5000 6000 0.45 0.5 0.55 0.6 Compressive Strength (psi) w/c Ratio Type 1 20% 40%

5 Figure 4. Comparison of Cement Type on Compressive Strength at 14 Days of Age 4. i. The figure below contains data from all of the mixtures prepared this semester as a graph for the ordinary concrete and the two fly ash concretes (fog room cured) showing the tensile strength of concrete (y-axis) at 7 days of age with the w/c of the mixture (x- axis). Figure 5. Tensile Strength of 7 Days of Age ii. The figure below contains data from all of the mixtures prepared this semester as a graph for the ordinary concrete and the two fly ash concretes (fog room cured) showing the tensile strength of concrete (y-axis) at 14 days of age with the w/c of the mixture (x- axis). 0 1000 2000 3000 4000 5000 6000 0.45 0.5 0.55 0.6 Compressive Strength (psi) w/c Ratio Type 1 20% 40% 0 50 100 150 200 250 300 350 0.4 0.45 0.5 0.55 0.6 0.65 Tensile Strength (psi) w/c Ratio Type 1 20% 40%

6 Figure 6. Tensile Strength of 14 Days of Age iii. a. The figure below contains data from all of the mixtures prepared this semester as a graph comparing the effect of cement type (ordinary Type I or cement/fly ash) on the tensile strength (y-axis) of fog cured concrete for each w/c at 7 days (the horizontal axis labels will be the four w/c ratios). Figure 7. Comparison of Cement Type on Compressive Strength at 7 Days of Age b. The figure below contains data from all of the mixtures prepared this semester as a graph comparing the effect of cement type (ordinary Type I or cement/fly ash) on the tensile strength (y-axis) of fog cured concrete for each w/c at 14 days (the horizontal axis labels will be the four w/c ratios). 300 400 500 600 700 800 900 0.4 0.45 0.5 0.55 0.6 0.65 Tesnile Strength (psi) w/c Ratio Type 1 20% 40% 0 50 100 150 200 250 300 350 0.45 0.5 0.55 0.6 Tensile Strength (psi) w/c Ratio Type 1 20% 40%

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7 Figure 8. Comparison of Cement Type on Compressive Strength at 14 Days of Age Discussion 1. The sources of error that could have affected the accuracy of the concrete testing are both human and experimental. The human error that could have occurred during this experiment could be accounted to tampering the concrete into the molds and when proportioning out the concrete into those same molds, as despite the best of efforts, it would be quite difficult to ensure that each mold had the same exact volume of concrete in each mold to have the same sizes. Almost all of the molds came out to the same dimensions in this laboratory experiment. Some of the experimental errors would mainly be due to the calculation errors with rounding the data. The overall semester data contained some values that were rounded and some that were not, and this could affect the accuracy of the average and standard deviation calculations, although very slightly. The standard deviation does seem to be fairly accurate when considering the compressive test results and figures provided above in the Results section of this laboratory report. Additionally, the 20% and 40% fly ash concretes (fog room cured) seem to increase their respective compressive strengths when cured for 14 days rather than 7 days, but the ordinary concrete (Type 1) seems to have very slightly decreased in compressive strength when cured for 14 days rather than 7 days. 2. For the mixture prepared by group B6-A, the calculated average compressive strength of the concrete is 4051 psi with a w/c ratio of 0.45 for the 14 days of age concrete, which seems to be on par with Figure 3 shows (which was provided in the laboratory instructions corresponding to this laboratory report) (Dai, 2023a). According to Figure 3, the expected value fir the compressive strength should be near 4 ksi (which equals ~4000 psi) for a concrete aged for 14 days with a w/c ratio of 0.45. The most likely cause of error for any inconsistency of results would most likely be attributed to the human error made when preparing the trail batch of concrete which could have had inconsistencies with measurements. This is especially true when considering that added materials during the slump testing the trail batch could have caused issues with measurements. 3. Using the plots generated in the Results section above in this laboratory report, the effect of the w/c ratio and age have a noticeable impact on the compressive strength of the 0 100 200 300 400 500 600 700 800 900 0.45 0.5 0.55 0.6 Tesnile Strength (psi) w/c Ratio Type 1 20% 40%

8 concrete. An increase in w/c ratio indicates that the compressive strength will generally decrease, and an increase in aging of the concrete (fog room cured) would generally increase the compressive strength of the concrete. The concrete being cured in air rather than in the fog room would have seemingly increased the compressive strength of the concrete, regardless of the age of the concrete. This can be concluded using Figure 3 from the laboratory instructions (Dai, 2023a) as reference. Air curing the concrete would have resulted in less moisture in the concrete during testing, as the fog room would help the concrete retain moisture, and Figure 3 from the laboratory instructions (Dai, 2023a) indicate that a lower w/c ratio would increase the compressive strength of concrete, regardless of concrete age. 4. The effect of the two rates of cement replacement by fly ash (both 20% and 40%) on the 7 day and 14 day compressive strength compared to the concreted containing only portland cement can be seen with the graphs attached above in this laboratory report in the Results section. Generally, for the 7 days of age concrete, it is shown that portland cement concrete is generally stronger than either fly ash cements regardless of the w/c ratio of any of the concretes tested in this laboratory through the semester. The 20% fly ash concrete also seems to have a higher compressive strength than the 40% fly ash for all w/c ratios other than the 0.45 w/c ratio concrete. This could be attributed to human error. Generally, for the 14 days of age concrete, it can be concluded from the graphs that despite decreasing in compressive strength as the w/c ratio increases, all types of concrete (regardless of ordinary, 20% or 40%) have generally similar compressive strengths. The only exception to this is the concretes with a w/c ratio of 0.55, where the 20% concrete is significantly higher in terms of compressive strength. Relative to the process of hydration, the main cause of this difference in strength gain in the short term is mainly due to the fly ash reducing the heat of hydration and the air content in the concrete. This can cause a decrease in compressive strength as the setting time of the concrete increases. For the long term concrete, it can be concluded that the increase in compressive strength can be attributed to the age of the concrete. 5. For the mixture prepared in this laboratory experiment, the average compressive strength is 4051 psi, and the average tensile strength is 620 psi. One method to estimate the tensile strength is to calculate 10% of a specimen’s compressive strength. In this case, 10% of 4051 psi is 405.1 psi, which would be the tensile strength calculated using the first method of estimation. This estimation method is inaccurate as it calculates the tensile strength to be 405.1 psi, which is significantly lower than the average tensile strength calculated of the specimen in this laboratory experiment (which would have been 15.3%). Therefore, this method of estimation is inaccurate. The second method to estimate a specimen’s tensile strength is to use the equation recommended by the American Concrete institute for predicting tensile strength. The formula is shown below. Tensile Strength = 𝑘𝑘 𝑆𝑆 ( 𝑓𝑓 𝑆𝑆 ) 0 . 5 In this equation, k t is 6.7 for normal strength concrete, and f c is the average compressive strength in psi. Using this second method, a sample calculation is provided below to determine the estimated tensile strength. Tensile Strength = 𝑘𝑘 𝑆𝑆 ( 𝑓𝑓 𝑆𝑆 ) 0 . 5 = (6.7)(4051) 0 . 5 = 426 𝑝𝑝𝑝𝑝𝑝𝑝 This estimate is also significantly lower than the average tensile strength of the specimen calculated in this laboratory experiment, but also slightly higher than the first estimation method. Based on these calculations and estimates, it would seem that the second estimation method for calculating the tensile strength of a specimen is also inaccurate. 6. Based on the plots generated in the Results section above in this laboratory report, w/c ratio can affect the tensile strength of the concrete tested in this laboratory experiment. For the 7 days of age concrete, the tensile strength seems to decrease continuously for the40% fly ash concrete as w/c ratio increases. For type 1, the tensile strength increases until the w/c

9 is 0.5, where the tensile strength then decreases as w/c ratio increases. For the 40% fly ash concrete, the tensile strength stays relatively even with slight increases until the w/c ratio is 0.55, and then decreases when the w/c ratio is 0.6. For the 14 days of age concrete, both the 20% and 40% fly ash concretes decrease in tensile strength as the w/c ratio increases, but the 14 days of age type 1 concrete acts similarly to the 7 days of age type 1 concrete. The 14 days of age concretes all have higher tensile strengths than the 7 days of age concretes, and this relationship could be attributed similarly to the compressive strength behaviors of the concretes. The rate replacement of cement with fly ash also seems to have a correlation, as an increase in fly ash, regardless of age, also decreases the tensile strength of the concrete. Conclusion The objectives of this experiment are to perform compression and splitting tensile strength tests, to draw conclusions regarding the influence of mixture design (w/cm, materials used), and concrete age on compressive and splitting tensile strength, and to characterize concrete using microscopy. This laboratory experiment has indicated that generally, an increase in w/c ratio in concrete would correlate to a decrease in compressive strength of the concrete. This is significant as it correlates to the workability of concrete. It is also important to be cautious with the amount of water used in concrete as well as the curing conditions of the concrete (fog room cured versus air cured), as too high of a water content would decrease the compressive strength and tensile strength of concrete. Another conclusion that can be drawn from this laboratory experiment is that the age of curing of concrete can increase the compressive strength and tensile strength of the concrete. This is not only shown in the laboratory results shown in this laboratory report, but also Figure 3 included in the laboratory handout (Dai, 2023a) . This is significant as stronger concrete would be more resilient, even if it is exposed to a higher water content.

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10 References Dai, S. (2023-a). Lab 5 – Hardened Concrete Properties.

11 Appendix

3020 Lab 5

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