Concrete Testing

Alex Jensen BRAE 433 11-18-2009 Lab 3/7 Concrete Mixing and Testing Labs Objective: The class was divided into three separate groups; each assigned to a separate water to cement ration. The goal was to become familiar with the procedure of mixing concrete, performing a slump test, and the process of testing the strength of concrete cylinders and beams. Mixing Team BAMF was assigned with the water to cement ration of .4. The team began with adding the recommended amount of water, cement, and aggregate by weight. A 2% moisture content in the sand was assumed and incorporated to the total weight of water added to the mix. After the recommended Table 1 Initial mixture by weight amounts of ingredients were added, additional water and cement needed to be Lab Three 0.40 Recommended Weights added to increase the workability of the Water 28 lb concrete. Table 1 shows the initial amount Cement 70 lb Sand 88.9 lb of material added to the mix. The final 138.4 lb mixture by weight is summarized in Table 2 Coarse Aggregate Table 2 Final Concrete Mixture Final 0.40 Weights Water 28 lb Cement 120 lb Sand 88.9 lb Coarse Aggregate 138.4 lb % Moisture 2 % Actual Sand 90.8 lb Actual Water 46.7 lb Total Weight 395.9 lb Total Volume 3.1 ft^3 Water:Cement 0.4

% Moisture Actual Sand Actual Water Total Weight Total Volume

2 90.7 26.2 325.3 2.2

% lb lb lb ft^3

and meets the requirement for the water to cement ration of .4. After the concrete was mixed, a slump test was performed to ensure that the concrete mixture was of adequate consistency. Team Figure 1 Example of 2 inch slump on .4 BAMF was able to achieve an acceptable 2 water to cement concrete inch slump. Forms To create the concrete beams, wooden forms were used. WD-40 was used to lubricate the forms. The team took extreme care not to get any lubricant on the reinforcing steel

Table 3 Steel diameter in Rectangular which was set into three of the six rectangular Beams beams. The six inch concrete cylinders were cast in plastic forms. Table 3 summarizes the Diameter Steel (in) effective diameter of the steel used reinforcing the Beam 1 0.249 three rectangular beams. 2 3

0.25 0.251

Testing: The beams and cylinders were allowed to cure for 28 days to allow them to reach their effective 28-day strength. For the reinforced and non reinforced beams, testing was conducted on the Baldwin testing machine in lab 4. The mode of failure for the non-reinforced beams was cracking and then sudden failure. Figure 2 Nonreinforced Beam shows how the beam failed suddenly at a given load. For the steel reinforced beams, the ultimate strength of Figure 2 Baldwin the beam was much Time (sec) higher. Figure 3 shows Testing Machine the strength curve of a reinforced concrete beam. The concrete yielded first within the elastic region of the Force (lbs

2000 1500 1000

500

0

0

0.02

0.04

0. 06

0.08

0.1

-500

Figure 3 Baldwin Test results for NR Beam .25 in Diameter Steel R einfo rc ed B eam 6000 5000 4000 3000 2000 1000 0 0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

T ime (sec)

strength curve, at time .75, the steel begins to yield. At time .25, the maximum load held by the beam is witnessed. When the strength curve drops off, the steel has failed. For the Cylinder testing, the Forney testing machine was used to determine the compressive strength of the six inch concrete cylinders.. For the higher water to cement ratio mixes, a shear failure was the main mode of failure. With Team BAMF's .4 mix, Figure 4 Testing Results for .250 in diameter reinforced beam columnar failure was observed due to a higher compressive strength in the concrete. Conclusion: With a smaller water to cement ratio, there is a larger achievable compressive strength in the Figure 5 Forney concrete. This is due to the fact that there are testing machine less voids filled by water during the set/curing Figure 6 Column Failure in .4 water to cement ratio

process. After the curing process is complete this water will evaporate and leave behind a void. The more voids in the mix, the weaker the concrete will be. Appendix A shows all tabulated calculations including the theoretical and actual strength for each test scenario.