San Francisco State University
School of Engineering
ENGR 200, Materials of Engineering
Laboratory 3
Concrete Compression Test
I. OBJECTIVES
The purpose of this experiment is to investigate the strength of a general purpose concrete at a specific
proportion of its constituents, and to study the effect of curing time on the strength of concrete.
Note: Please refer to course handout for further reading on concrete.
II. EXPERIMENTAL PROCEDURE
Materials
Portland Cement, Sand, Gravels, Water.
Table 1: Proportion of constituent materials
Constituent
Cement
Sand (Fine Aggregate)
Gravels (Coarse Aggregate)
Water
Weight Ratio
1
1.8
2.7
0.65
Total Weight (lbs)
20
36
54
13
Apparatus
Bucket, metal rod, measuring tape, brick trowel, shovel, scale
Wheelbarrow
Slump Cone (12” height, Figure 1)
4 x Test Cylinders (6” diameter x 12” height)
Compression Tester
Concrete Preparation Procedure
1) Table 1 indicates that sufficient amount of concrete mix will result from
using approximately 20 lbs of cement
Figure 1. A slump cone.
2) Slowly add aggregates and cement into a wheel barrow, mix thoroughly
and then pour water. Mix concrete until it reaches a reasonable consistency.
3) Next, perform Slump Test as described below and in Figure 2:
i) Wet the cone with water and put it in an upright position with the bigger base flat down against a
pan. Fill a third at a time and poke a stick into the concrete 10-20 times all around it each time to
compact the mixture, i.e. there should be no air pockets inside, especially near the walls.
ii) After the cone is completely filled, lift it slowly counting 5 to 10 seconds for removal.
iii) Let the concrete settle for 60 seconds after the cone is completely removed.
iii) Measure how much the pile has slumped from the 12” original position
If slump is more than 3.5” (i.e. pile height is below 8.5” mark), add more fine and coarse aggregate
in equal amounts and repeat the slump test. If slump is less than 2.5” (i.e. pile height is above 9.5”
mark), add water and cement at the ratio of 0.60:1 and repeat slump test, until slump falls in
specified range (between 8.5” and 9.5” mark)
4) After passing the Slump Test, fill four Test Cylinders with the concrete mix, make sure to compact
the content to remove air bubbles by repeating the action in 3 (i). The top surface of the concrete should
be even and flush with the edge. Seal the cylinders properly.
(a)
(b)
(c)
Figure 2. Slump Test. (a) Pour concrete mix into slump cone. (b) Slowly remove slump cone. (c) Let
concrete pile sits for 60 seconds, and measure the slump (i.e. distance from original height). (Source:
http://upload.wikimedia.org/wikipedia/commons/archive/1/12/20070616102812!Slump_test.png)
III. COMPRESSION TEST & DATA COLLECTION
Compression Test: To measure the strength of hardened concrete. This test will be carried out over a
period of 4 weeks, starting one week after the concrete has been mixed.
1) Four compression tests will be carried out to determine the compressive strength of the concrete as a
function of curing time. The first test will be performed one week from today, followed by one test per
week in the subsequent three weeks.
2) Place a specimen in the concrete tester and adjust the compression head clearance to bring it in
contact with the specimen
3) Place the red follow marker on the load indication face to zero
4) Activate the load cell by selecting the appropriate valve position and pump on the hydraulic cylinder
using the manual lever fitted to the side. Continue until failure of the specimen occurs.
5) Record the fracture strength values (Note: you will record 4 values, corresponding to the fracture
strengths at the end of Week 1, 2, 3, and 4)
IV. DELIVERABLES FROM YOU
1. Lab Assignment: Answer questions in (2) below and turn in a Tech Memo on the designated date,
after you have completed 4 weeks of compression tests.
2. Please answer the following questions:
i) Why is it important that during the first few days of the curing of concrete the evaporation of
water from its surface be prevented or reduced?
ii) What is the disadvantage of too high a water-cement ratio? What is the disadvantage of too low a
water-cement ratio?
iii) What happens to the compressive strength of the concrete between 7 to 28 days? Plot a graph of
“Compressive Strength (Psi)” vs. “Time (week)”, label it as Figure 1 and discuss the trend observed.
iv) How does the compression test result compare to expected value at the end of 28 days, as
illustrated in Figure 3 (below), based on the water-to-cement ratio of your sample?
v) How do the aggregates affect the mixture? Discuss the effects of having too much and too little
aggregates.
vi) Suggest possible chemical bondings involved in concrete forming. Briefly explain your answer.
Figure 3. Effect of water-to-cement ratio by weight on the compressive strengths of normal and airentrained concrete at the end of 28 days.
San Francisco State University
School of Engineering
ENGR 200, Materials of Engineering
Data Sheet for Experiment on
Lab 03: Concrete Mixing and Testing.
Group Members: ________________________________________________________
Date: _______________
Constituents:
Constituents
Weight
(lbs)
Adjustment
Weight
(lbs)
Total
Weight
(lbs)
Cement
Sand
Gravel
Water
Slump Test on Wet Concrete: (between 2.5-3.5 in)
Final Slump (in)
Compression Tests on Hardened Concrete:
Curing Time (Week)
One Week
Two Weeks
Three Weeks
Four Weeks
Compressive Load (lbf)
Filename:
200-Lab3-Concrete Test
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