Aggregates perform different purposes in Civil Engineering, including functioning as component materials for Portland cement concrete, hot mix asphalt, and bounding foundation layers beneath buildings and pavements. Natural aggregates consist of individual granular materials obtained from natural deposits, such as river run deposits, quarrels, or gravel pits. Particle shape and texture; absorption; bulk gravity; soundness and durability; bulk unit weight’ and gradation and maximum size form the most essential properties of aggregate investigated in the experiment. Concrete is a mixture of cement, water, and aggregate. 60-70 percent of the volume of concrete and approximately 80 percent of the weight of concrete are made up of aggregate (Prowell, Jingna, and Brown 12).
Engineers have come up with different equations used to calculate the properties of aggregate. Laboratory tests have been used to prove these equations, and the following report conducts several tests to investigate different properties of aggregate as mentioned above.
Sieve Analysis of Fine and Coarse Aggregate
Sieve analysis forms the basic essential test for determining the gradation of aggregates. The main properties investigated in this test are the particle size. The particle size of the aggregate is given as a percentage of weight retained between consecutive sieves used in the test as shown in equation 1.
Percentage particle size = ……………………………… 1
Dry-Rodded unit Weight of Aggregate
Dry rodded unit weight of aggregate is determined by compacting dry aggregate into a test container of a known volume as per ASTM C 33 gradation number. The dry rodded weight is obtained by dividing the weight of the aggregate by the volume of the container. Equation 2 shows how dry rodded weight is calculated theoretically.
Dry Rodded unit weight = ………………………………….2
Where; W2 – Total weight of the proctor mole and the base plate
W1 – sum of weights of the mold, the base plate and dry rodded coarse aggregate.
Moisture Content of Stored Aggregate
Moisture content is the percentage of water found in a given volume of aggregate. The moisture content of an aggregate helps in developing the perfect water/cement ratio to use when making concrete. Each aggregate contains a specific percentage of moisture that depends on the porosity of particles making up the aggregate and the moisture condition of the storage area. Moisture content of aggregate is given by equation 3 below:
Moisture content of Aggregate (%) = …………………….………..3
Where: W1– Weight of dry pan
W2 – Weight of pan and moist aggregate
W3 – Dry weight of aggregate sample and pan
Bulk Specific Gravity and Water Absorption of Fine Aggregate
Bulk unit weight represents the dry weight of compacted aggregate occupying a specific bulk volume. Water absorption of the aggregate is the rate at which an aggregate draws water from a container of a specific volume. Water absorption is important in the construction because it provides an Engineer with the idea of the specific dry-time of concrete. It is calculated using the formula shown in equation 4 below:
Water absorption = ………….4
The bulk specific gravity is calculated as:
Bulk Specific gravity = ………5
The experiment was conducted in two parts. Part I involved sieve analysis and bulk rodded unit weight determination while part II investigated the moisture content, bulk specific gravity and absorption capacity of the aggregate. The objectives of part I was to determine the gradation and dry rodded unit weight of coarse aggregate of coarse and fine aggregate to be used in making concrete mix using. The objective of part II was to determine the bulk specific gravity, moisture content of stored material, and absorption of coarse and fine aggregate to be used in making a concrete mix.
PART I: Sieve Analysis and Bulk Rodded Unit Weight Test
Equipment and Materials
- Dry, coarse and fine aggregate
- Weigh balance
- Proctor mold with base plate and extension shovel
- (5/8) Inch) Tamping Rod with hemispherical tip
- Sieves and an electric sieve shaker
Test 1: Sieve Analysis of Coarse Aggregate
- Approximately 2.5 Kg of air dry aggregate was weighed (test sample).
- The appropriate sieve sizes that represented all particle sizes were selected. The selected sieves were 1”, ¾”, 3/8”, ¼”, and #4 sizes and a pan. All the sieves were pre-weighed and the results recorded in table 1. The sieves were sorted and arranged in a descending order with the pan at the bottom to hold the last particles.
- The pre-weighed sample of the aggregate was placed in the upper sieve and sieve-shaker operated for ten minutes.
- The weights of retained aggregate in each sieve and in the pan were determined and recorded in table 1.
- The total sum of the retained weights was checked to correspond to the original sample weight. Difference between the weights showed that a correction factor would be applied
- The percentage of aggregate retained in each sieve was calculated using the equation 1 above
- The cumulative percentage aggregate retained and aggregate passing for each sieve was also calculated
- A graph of finer versus grain size was plotted, and ASTM C 33 scale used to identify the size number of the course aggregate used in the sieve analysis test.
Test 2: Sieve Analysis of the Fine Aggregate
- A test sample of the fine aggregate was weighed as shown in step 1 in test 1
- The sieve sizes used for this test were #4, #8, #16, #30, #50, and #100. The sieves were arranged in an ascending order so as to compute the finest modulus.
- Steps 3 to 8 in test I were followed and the determined values recorded in table 2.
Test 3: Dry Rodded Unit Weight of Coarse Aggregate
- Ten ponds of air-dry coarse aggregate were obtained from the sample
- The proctor mold of 3.07 liters with a base plate and an extension was obtained
- The weights of the proctor mode and the base was measured and recorded in table 3. (W1)
- An extension was attached to the top of the proctor mold that seated in the base plate as shown in figure 1
Figure 1: A mould with base plate and extensions used for test 3
- The coarse aggregate was placed in three equal layers. Each layer was rodded with a 0.625 inches (0.016m) diameter rod, with an hemispherical tip, 25 times
- The extension was removed from the mode and a straight edge used to trim the excess aggregate above the mold
- The sum weights of the mold, the base plate and the dry rodded coarse aggregate were measured (W2). The figures obtained were recorded in table 3.
- The dry rodded weight was calculated using equation 2
PART II: Moisture content, Bulk Specific Gravity & Absorption Capacity
- Absorption cone (mold) and corresponding tamping rod
- Absorbent Towels/blankets
- Aspirator and Fine aggregate
- Coarse and Fine Aggregate
- Weighing balance
- Distilled water
- 500 ml flask
- Metal frame and basket for submerging aggregate samples
- Water tank (5 gallon basket)
Test 4: Moisture Content of Stored Aggregate
- The pan was weighed and its weight recorded (W1)
- A sample of aggregate was places in the pan, and the weight of the pan together with a sample taken (W2)
- The pan and the moist aggregate were placed in an oven for 24 hours. After the end of 24 hours, the dry weight of the aggregate sample plus the pan was taken (W3)
- The moisture content of the aggregate sample was calculated using equation 3.
- The procedure was repeated using coarse aggregate sample and its moisture content calculated
Test 5: Bulk Specific Gravity and Water Absorption of Coarse Aggregate
- A coarse aggregate was obtained and soaked in water for 24 hours to ensure it was fully saturated. The excess water was carefully decanted in order not to lose any aggregate. The sample was placed on a flat surface exposed to a gently moving current of warm air and stirred frequently
- The sample was dried to the saturated surface-dry condition (SSD) using a towel. Care was taken not to over-dry the sample
- 2 kg of SSD aggregate was obtained from the dried sample (A)
- The weight of metal frame with the basket submerged in water without aggregate was obtained and recorded (D)
- The weight of SSD aggregate and metal frame submerged in water was obtained and recorded (E)
- The entire sample of coarse aggregate was removed from the metal frame and emptied into a pan. The sample was then placed in the oven for 24 hours. The weight of the pan was recorded. In addition, the weight of the oven dry aggregate was taken and recorded (B)
- The weight of SSD aggregate submerged in water (C) was taken as follows: C = (E – D)
- The bulk specific gravity was calculated using equation 5
- The absorption at SSD condition was calculated using equation 4.
Test 6: Bulk Specific Gravity and Water Absorption of Fine Aggregate
- A sample of fine aggregate was obtained and soaked in water for 24 hours to ensure saturation. The excess water was carefully decanted in order not to lose any aggregate. The sample was placed on a flat surface exposed to a gently moving current of warm air and stirred frequently
- The sample was dried to the saturated surface-dry condition (SSD) taking care not to over-dry. The SSD condition was determined by a cone test as follows:
- The cone was filled with fine aggregate
- A tamping rod was used to lightly rod the fine aggregate 25 times with a drop height of 2 inches
- The cone was then gently lifted from the sample
- SSD condition was the point at which enough moisture had evaporated from the drying process that allowed the fine aggregate sample to fail when the cone was removed
- After identifying the SSD condition of fine aggregate, two samples were obtained. The first sample weighing 250 grams was used to determine the absorption capacity of fine SSD aggregate while the second sample weighing 100 g was used to determine bulk specific gravity.
- The 250 grams sample of SSD fine aggregate (W4) was taken and the sample emptied into a pan and placed in the oven for 24 hours. The weight of dry oven was pre-determined (W5)
- The absorption at SSD condition was calculated as Absorption (SSD) = (W4 –W5)/ W5
Test 8: Bulk Specific Gravity
- A 500 ml flask was filled with distilled water and its weight recorded as (W6)
- The water was emptied into another container
- The 100 grams sample of SSD fine aggregate was placed into the flask and the bulb of the flask filled to two thirds full with distilled water
- An aspirator was used to remove all air from the sample for 15 minutes until all air bubbles disappeared. The process termed as de-aeration
- The flask was then filled with distilled water to the 500 ml mark and its weight recorded (W7) W7 = (weight of de-aired material + weight of distilled water to 500 ml mark + weight of the flask)
- The entire content was emptied into the pan. A squeeze bottle was used to wash out all remaining particles adhered to the flask into the pan
- The pan and its components were placed in the oven for 24 hours. After the drying period the weight of the dry aggregate together with the pan was taken (W8)
- The bulk specific gravity of fine aggregate was calculated as
Bulk specific gravity = …………………………..6
Results and Calculations
Table 1: Course aggregate sieve analysis
|Sieve No.||Size (mm)||Sieve Weight (lb)||Sieve weight
|Corr. factor||Corr. weight||% Retained||Cum. % Retained||% Cum. Finer|
Sample initial weight
|Sample final weight||Sample corrected weight|
W0 = 5.502
|Wf = 5.502
|Wc = 5.502
Figure 1: A graph of percentage finer versus grain size of the coarse aggregate sample
Table 2: Fine aggregate Sieve analysis
|1||2||3||4||5 = 4-3||6*||7 = 5+6||8 = (7/W0)*100||9||10 = 100-9|
|Sieve No.||Size (mm)||Sieve Weight (lb)||Sieve weight (W/Agg)||Aggregate Weight (lb)||Corr. factor||Corrected weight||%
|Cum. % Retained||% Cum. Finer|
|#8||2.36||1.06||1.066||0.006||1.3 * 10-5||0.0060013||0.11||0.11||99.89|
Sample initial weight
W0 = 5.50
Wf = 5.488
Wc = 5.5
Figure 2: A graph of percentage finer versus grain size of the fine aggregate sample
Correction factor = x Column 5 NB: Wo = Wc
Table 3: Dry Rodded Unit Weight of Coarse Aggregate
|Mold Weight (in)||Mold Diameter (In)||Volume
|Dry Rodded Unit Weight
|Mold Weight (mm)||Mold Diameter (mm)||Volume
|Dry Rodded Unit Weight (N/MM3)|
(Dry rodded Unit weight in N/mm3) =
= = 13585.95 N/mm3
Table 4: Moisture content of coarse aggregate results
|W1 (lb)||W2 (lb)||W3 (lb)|
Moisture content % = W% (W2-W3)/(W3 – W1)* 100 = (0.534-0.516)/(0.516-0.138)
W% = 1.31%
Table 5: Moisture content of fine aggregate results
|W1 (lb)||W2 (lb)||W3 (lb)|
Moisture content (W %) = W% (W2-W3)/(W3 – W1)* 100 = (0.588-0.57)/(0.57-0.096)
W % = 3.797%
Table 6: Absorption capacity of coarse aggregate
|W1 (lb)||W2 (lb)||W3 (lb)|
Absorption capacity (S %) = (W2-W3)/W3-W1) *100
S % = (1.516-1.738)/1.768-0.132) = 3.59%
Table 7: Absorption capacity of fine aggregate results
|W1 (lb)||W2 (lb)||W3 (lb)|
Absorption capacity (S %) = (W2-W3)/W3-W1) *100
S% = (0.314-0.314)/(0.314-0.1) = 0%
Table 8: bulk specific gravity of fine aggregate
|W1 (lb)||W2 (lb)||W3 (lb)||W4 (lb)||W5 (lb)
|Bulk Specific gravity|
Bulk Specific gravity -=
= = 2.625
Questions for Part I
What type of Gradation was Obtained for Both Fine and Coarse Aggregate?
The coarse aggregate sieve test obtained a gap graded gradation. The graph shown in figure 1 clearly indicates that the particle sizes of the coarse sample tested had some deficiency. The curve does not represent a good representation of all particles sizes as it shows more concentration on the larger sieves, an indication that a small percentage of particles were retained in the larger sieves.
On the fine aggregate test, the particle sizes were well graded. The curve in figure 2 demonstrates a good representation of all particle sizes in all sieves. The percentage of particles retained in each sieve was almost equal making a uniformly graded aggregate.
Does the Coarse Aggregate Meet the Grading Requirements of One of the ASTM C 33 Ranges?
The coarse aggregate passed the grading requirements of 1” sieve. From table 1, the cumulative percentage that passed through sieve (1”) was 95.2%. The gradation requirements for coarse aggregate (ASTM C 33) requires that the cumulative percentage of aggregate passing be in the range of 90-100. The aggregate passed the gradation number 56 with a 25 mm sieve.
Why is the ASTM C 33 Coarse Aggregate Size Number Important?
The ASTM C33 coarse aggregate size number acts as the most effective method of grading a coarse aggregate because it is compatible with most aggregate particle sizes and determines the best coarse aggregate for making a good concrete.
What is the Fineness Modulus an Indication of and Why is it only Determined for Fine Aggregate?
Presence of the fineness modulus indicates that the concrete will equal proportions of cement, water and sand. Fineness modulus tests are performed only on fine aggregates because a change in fine aggregate significantly affects concrete properties (Gambhir 86).
What is the Fineness Modulus of the Fine Aggregate?
The finest modulus helps in estimating the proportion of fine and coarse aggregates in concrete moisture. The parameter helps engineers in estimating the best proportions of water cement and aggregate while making concrete and establish the best design depending on the particle sizes of the aggregate (Gambhir 86).
Describe the Physical Properties of the Aggregates
The aggregates used in the experiment had a fine texture. The aggregates were also hard because the dry rodded unit weight of 0.053 lbs per cubic inch was obtained. The results indicated that the test team experienced difficulties in compacting aggregates. The aggregates were non-porous. A low moisture content averaging 3 percent indicated that the aggregate was less porous and allowed less water to infiltrate through.
Effects of Physical Properties of Aggregate on the Final Concrete Product?
Physical properties of aggregates play an important role in the strength and durability of concrete. The size of the particles affects the volume and quantity of other materials like cement, sand and water used to make concrete. Fine aggregates lead to less void in a concrete and the lesser the quantity of other materials. On the other hand, the physical properties of concrete affect the quality of concrete by influencing the settling time. For instance, concrete made from porous aggregate takes less time to settle because the availability of poles allows circulation of air that fastens drying.
Differences Between Specific Gravity, Bulk Specific Gravity (Dry), and Bulk Specific Gravity (SSD)
Specific gravity is the ratio of the density of a substance to the mass of the same unit volume. Bulk specific gravity (dry) refers to the ratio of a specific volume of dry compacted aggregate to the weight of an equal volume of water. Moreover, bulk specific gravity (SSD) is the ratio of saturated dry aggregate to the mass of equal volume of water. The three properties of aggregate have significant differences. The bulk specific gravity (dry) determines the density of dry aggregate with no water while the specific gravity makes use of water to determine the density of the aggregate (Prowell, Jingna, and Brown 66).
When the moisture content is greater than the absorption capacity, less water should be added to the concrete mix. High moisture content indicates that the aggregate has more water; while a low absorption capacity indicates that the aggregate attracts water slowly. Adding more water will make the mixture soak fast. On the other hand, a lesser moisture content than the absorption rate requires adding more amount of water to the concrete mixture. The high volume of water added will allow the mixture to soak fast before the available water evaporates due to low moisture content.
The value of bulk specific gravity for the fine aggregate was 2.625 while that of the coarse aggregate was not tested. The bulk specific gravity obtained for the fine aggregate was not close to the theoretical value of 1.44. The tested value exceeded the theoretical value by (2.625-1.44) 1.185. The theoretically known value for the bulk specific gravity for coarse aggregate is 1.60.
Bulk specific gravity is mostly used in concrete mix design computations because it shows the percentage of voids in the aggregate and makes the constructor understand the ratio of other materials that will make a quality mix. The normal specific gravity calculation involves the total volume of the aggregate including the voids and does not give the exact character of the aggregate material used in making a concrete mix.
Failure to dry the particles to the saturated-dry state leaves some moisture in the aggregate sample. The following problem affects the value of bulk specific gravity, SSD. A higher than the true value is obtained because the gravel does not lose all the water through drying that makes it heavier, but the volume remains constant. Increased mass with a constant value of volume leads to a high bulk gravity.
The laboratory experiment experienced some errors as listed below:
- Weighing errors because of fault weighing balances
- Failure to dry the sample to saturation dry weight when testing the bulk specific gravity (dry) and (SSD)
- The tests were not allowed to dry for the whole 24 hours as expected
- Fault experiment apparatus that provided false results leading to errors
One of the major purposes of aggregate of importance to this research is making concrete. Physical properties of aggregate help constructors in determining the best aggregate to use in a concrete mixture. Aggregate influences concrete properties because it accounts for larger volume in the mixture. The results obtained from this research help in recommending the best aggregate materials to use while making a concrete mix for ASTM C33 gradation.
- Gambhir, Murari L. Concrete Technology: Theory and Practice. , 2013. Print.
- Prowell, Brian D, Jingna Zhang, and E R. Brown. Aggregate Properties and the Performance of
- Superpave-Designed Hot Mix Asphalt. Washington, D.C: Transportation Research Board, 2005. Print.