Reference no: EM132870387

Lab - Hardened Properties of Portland Cement Concrete

Objectives

The purpose of this experiment is to:
• Determine the compressive strength of concrete samples produced in Lab 7.
• Determine the split tensile strength of concrete samples produced in Lab 7.
• Determine the elastic modulus of concrete samples produced in Lab 7.
• Determine the unit weight of concrete samples produced in Lab 7.
• Determine the ultrasonic pulse velocity (UPV) of concrete samples produced in Lab 7.
• Examine the statistical variability in the results.
• Determine the effects of w/c ratio and hydration time on concrete hardened properties.
• Evaluate the correlations between strength, modulus, w/c ratio, unit weight, and UPV.

Analysis of Results and Discussion

For the analysis, you will need to analyze all of the data collected from all lab sections. You will make 2 Tables and 15 Figures in the Results section (Note: make sure to include all tables and figures).

Analysis of Your Lab Section Data

a) From the dataset, calculate the average 35-day compressive strength, split tensile strength, elastic modulus, and UPV. Do this for each of the 3 mixes. Create a summary table - call it Table 1 - with these results. Also include the w/c ratio, initial slump, and final slump in this table. Comment on the trends and relationships. Does w/c ratio correlate with the hardened concrete properties? Do the initial or final slump appear to relate to the hardened concrete properties? Why or why not?

b) Create another data summary table - call it Table 2 - that includes the coefficient of variation (COV) for the 35-day compressive strength, split tensile strength, elastic modulus, and UPV. COV is the standard deviation divided by the average. Represent COV as a percent value. Comment on the variability of the various hardened concrete properties. Which property or properties have the greatest variability and why? Do you expect these trends? Why or why not?

c) Create 3 figures - Figures 1, 2, and 3 - one for each concrete mix - of the compressive strength (y axis) vs. age (x axis in days). Plot all data (not the averages). Try to find an equation to fit the data, such as a log or ln relationship. Comment on the trends. Does concrete gain strength linearly or nonlinearly with time?

d) Create 3 figures - Figures 4, 5, and 6 - one for each concrete mix - of the compressive strength (y axis) vs. hardened unit weight (x axis) for all ages. Plot all data (not the averages). Try to find an equation to fit the data. Comment on the trends. Is concrete compressive strength correlated to unit weight? Why or why not?

e) Create 1 figure - Figure 7 - as a combination of all data from Figures 4, 5, and 6. Plot all data (not the averages). Try to find an equation to fit the data. Is concrete compressive strength correlated to hardened unit weight irrespective of w/c ratio? Why or why not?

f) Create 3 figures - Figures 8, 9, and 10 - one for each concrete mix - of the compressive strength (y axis) vs. UPV (x axis) for all ages. Plot all data (not the averages). Try to find an equation to fit the data. Comment on the trends. Is concrete compressive strength correlated to UPV? Why or why not?

g) Create 1 figure - Figure 11 - as a combination of all data from Figures 8, 9, and 10. Plot all data (not the averages). Try to find an equation to the fit the data. Is concrete compressive strength correlated to UPV irrespective of w/c ratio? Why or why not? Would you use UPV to accurately predict compressive strength in the field?

h) A common empirical correlation equation for elastic modulus is: where E is the elastic modulus in psi, UW is the hardened unit weight in lb/ft3, and fc' is the compressive strength in psi. Use this equation to predict the elastic modulus for all cylinders where elastic modulus and compressive strength were measured. On 1 figure - Figure 12 - plot predicted E (y axis) vs. measured E (x axis) for each of the 3 mixes. Try to find an equation to fit the data - there should be 3 different fits - one for each mix. Did the equation overpredict or underpredict the elastic modulus? For design purposes, would it be better to use an equation that will overpredict or underpredit the elastic modulus based on the compressive strength?

i) For elastic, homogeneous, and isotropic materials: elastic modulus, ρ is the density (assume for simplicity that it is equivalent to unit weight), and v is Poisson's ratio (assume 0.2 for simplicity). (Hint: for the UPV equation, it is easier for unit cancellation to have UPV in m/s, E in Pa, and ρ in kg/m3). Use this equation to predict the elastic modulus for all cylinders where elastic modulus and UPV were measured. On 1 figure - Figure 13 - plot predicted E (y axis) vs. measured E (x axis) for each of the 3 mixes. Try to find an equation to fit the data - there should be 3 different fits - one for each
mix. Did the equation overpredict or underpredict the elastic modulus? Does UPV appear to be a good predictor of elastic modulus? Why or why not?

j) On one figure (Figure 14), plot the UPV vs. time for each mix. There should be 3 distinct datasets, so include a legend. Plot all data (not the averages). Try to find an equation to fit the data. Comment on the trends. Does UPV increase or decrease over time? Why or why not? Discuss if experimental data agrees with the expected trends.

k) On one figure (Figure 15), plot the hardened unit weight vs. time for each mix. There should be 3 distinct datasets, so include a legend. Plot all data (not the averages). Comment on the trends. Does hardened unit weight increase or decrease over time? Compare the hardened unit weight values to the fresh concrete unit weight from Lab 7. Is there a difference between fresh and hardened concrete unit weight? Why or why not?

Discussion Questions

A. If you were an engineer in the field designing and mixing concrete, would you use slump as a predictor of concrete strength (consider initial and final slump)? Would you use UPV as a predictor of strength? Would you use unit weight as a predictor of strength? Justify your answer based on your findings.

B. One common empirical correlation relationship, where compressive and split tensile strengths are in units of psi. From the data you tabulated in Table 1 in Section 6, compare the measured split tensile strength to the predicted split tensile strength from this equation. Is the split tensile strength overpredicted or underpredicted by this equation? For a design problem, would you prefer to overpredict or underpredict the split tensile strength? Why or why not?

C. What design compressive strength of a concrete column would you be comfortable using each of these 3 mixes for? Assume that your measured 35-day compressive strength is 85% of the ultimate strength. Assume a 20% factor of safety. Round your answer to a reasonable precision of 100 psi (hint: for a design strength, should you round to the nearest high or low 100 psi?...).

D. Why does concrete exhibit such a large statistical variability in concrete cylinder strengths, even though they were all made from the same mix? How does the concrete strength variability compare to the variability in yield strength for the steel and aluminum specimens in Lab 3?
E. For the Lab 9 demonstrations, comment on the various non-destructive testing (NDT) techniques by completing the following table. Discuss one or two advantages, one or two disadvantages, and one or two application scenarios where you would use these techniques. The application scenarios can be general or specific.

Attachment:- Lab Hardened Concrete.rar