Alex JensenBRAE 43311-18-2009

Lab 3/7Concrete 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.

MixingTeam 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 amounts of ingredients were added, additional water and cement needed to be added to increase the workability of the concrete. Table 1 shows the initial amount of material added to the mix. The final mixture by weight is summarized in Table 2

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 BAMF was able to achieve an acceptable 2 inch slump.

FormsTo 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

Water 28 lbCement 70 lbSand 88.9 lbCoarse Aggregate 138.4 lb% Moisture 2 %Actual Sand 90.7 lbActual Water 26.2 lbTotal Weight 325.3 lbTotal Volume 2.2 ft^3

Lab Three 0.40 Recommended Weights

Water 28 lbCement 120 lbSand 88.9 lbCoarse Aggregate 138.4 lb% Moisture 2 %Actual Sand 90.8 lbActual Water 46.7 lbTotal Weight 395.9 lbTotal Volume 3.1 ft^3Water:Cement 0.4

Final 0.40 Weights

Table 1 Initial mixture by weight

Table 2 Final Concrete Mixture

Figure 1 Example of 2 inch slump on .4 water to cement concrete

which was set into three of the six rectangular beams. The six inch concrete cylinders were cast in plastic forms. Table 3 summarizes the effective diameter of the steel used reinforcing the three rectangular beams.

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 shows how the beam failed suddenly at a given load. For the steel reinforced beams, the ultimate strength of the beam was much higher. Figure 3 shows the strength curve of a reinforced concrete beam. The concrete yielded first within the elastic region of the

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,

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 concrete. This is due to the fact that there are less voids filled by water during the set/curing

Beam Diameter Steel (in)1 0.2492 0.253 0.251

Table 3 Steel diameter in Rectangular Beams

Figure 3 Baldwin Test results for NR Beam

Figure 4 Testing Results for .250 in diameter reinforced beam

Figure 2 Baldwin

Figure 5 Forney testing

Figure 6 Column Failure in .4 water to

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.