Compressive Strength Analysis of Concrete made with Demolished Aggregate within acceptable strain limit of Concrete.
1.1 Introduction
Concrete used for residential purposes is around 2,500 psi (17 MPa), 4,000 psi (28 MPa) for commercial uses, and as high as 10,000 (70 MPa) for other specified applications. As the world population increases, the use of natural resources and energy grows proportionally. One of the major environmental concerns today is related to the excessive consumption of natural resources. The search for a solution to this problem is already under way in several sectors. One of the sectors with a major responsibility here is the construction industry, due to its use of natural resources and the amount of waste that is created, related to concrete use, the demolition of concrete structure produces waste that is difficult to store owing to the lack of proper dumping places and high transportation and storage costs.
1.2 Background of the Study
In Bangladesh, the volume of demolished concrete is increasing due to deterioration of concrete structure as well as the replacement of many low-rise building by relatively high-rise building due to booming of real estate business. Disposal of demolished concrete is becoming a great concern to the developers of the buildings. If demolished concrete can be used for new construction, the disposal problem will be solved, the demand for new aggregate will be reduced, and finally the consumption of natural resources for making aggregate will be reduced.
1.3 Objectives of the Study
The main objectives of the study are:
1. To analyze the compressive strength of concrete.
2. To analyze the stress-strain behavior of concrete.
3. To investigate the workability of concrete.
1.4 Methodology
The aggregate samples were collected from five different locations in Dhaka city. Physical test
Like, Sieve analysis, Abrasion test, Specific gravity & Absorption capacity, Unit weight and
voids were performed for recycled brick aggregates.
Waste concrete was acquired and crushed to the desired particle size in the laboratory. After some physical test of aggregate, the molds were prepared for destructive test in “Universal Testing Machine”. Strains were measured by strain gauge. Finally, with all the data found from destructive test, stress strain curve drawn.
After designing the concrete mix, batches of concrete mix were casted into 4” X 8” standard cylindrical molds are cured. Loading was 4KN/sec applied by the Universal Testing Machine over the specimens. Stress-Strain was measured for each case. Crashing pattern and crack surface picture were taken for the specimens. Strains were measured by strain gauge. Then test results tabulated and converted in a graph.
LITERATURE REVIEW
2.1 Introduction
Compressive strength analysis is most important to select the coarse aggregate. Most importantly cement, sand and aggregate properties with mixing procedure discussed in this chapter. Water, admixture details, curing, compressive strength calculation also performed.
2.2 Cement
Cement is a cementing of bonding materials and water-resistant product used in engineering construction. Portland cement was developed from natural cements made in Britain in the early part of the nineteenth century, and its name is derived from its similarity to Portland stone, a type of building stone that was quarried on the Isle of Portland in Dorset, England.
The Portland cement is considered to originate from Joseph Aspdin, a British bricklayer from Leeds. It was one of his employees (Isaac Johnson), however, who developed the production technique, which resulted in more fast-hardening cement with a higher compressive strength. Portland cement (often referred to as OPC, from Ordinary Portland Cement) is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout. It is a fine powder produced by grinding Portland cement clinker (more than 90%), a limited amount of calcium sulfate (which controls the set time) and up to 5% minor constituents as allowed by various standards such as the European Standard EN197.1:
Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates (3CaO.SiO2 and 2CaO.SiO2), the remainder consisting of aluminum- and iron-containing clinker phases and other compounds. The ratio of CaO to SiO2 shall not be less than 2.0. The magnesium oxide content (MgO) shall not exceed 5.0% by mass.
ASTM C 150 defines Portland cement as “hydraulic cement (cement that not only hardens by reacting with water but also forms a water-resistant product) produced by pulverizing clinkers consisting essentially of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulfate as an inter ground addition.” Clinkers are nodules (diameters, 0.2-1.0 inch [5–25 mm]) of a sintered material that is produced when a raw mixture of predetermined composition is heated to high temperature. The low cost and widespread availability of the limestone, and other naturally occurring materials make Portland cement one of the lowest-cost materials widely used over the last century throughout the world. Concrete becomes one of the most versatile construction materials available in the world.
Portland cement clinker is made by heating, in a kiln, a homogeneous mixture of raw materials to a sintering temperature, which is about 1450 °C for modern cements. The aluminum oxide and iron oxide are present as a flux and contribute little to the strength. For special cements, such as Low Heat (LH) and Sulfate Resistant (SR) types, it is necessary to limit the amount of tricalcium aluminates (3CaO.Al2O3) formed. The major raw material for the clinker making is usually limestone (CaCO3) mixed with a second material containing clay as source of alumina-silicate. Normally, an impure limestone, which contains clay or SiO2, is used. The CaCO3 content of these limestones can be as low as 80%. Second raw materials (materials in the raw mix other than limestone) depend on the purity of the limestone. Some of the second raw materials used are: clay, shale, sand, iron ore, bauxite, fly ash and slag. When a cement kiln is fired by coal, the ash of the coal acts as a secondary raw material.
2.3 Aggregate
Construction aggregate, or simply “aggregate“, is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete. Aggregates are a component of composite materials such as concrete and asphalt concrete; the aggregate serves as reinforcement to add strength to the overall composite material. The American Society for Testing and Materials publishes an exhaustive listing of specifications for various construction aggregate products, which, by their individual design, are suitable for specific construction purposes. These products include specific types of coarse and fine aggregate designed for such uses as additives to asphalt and concrete mixes, as well as other construction uses. State transportation departments further refine aggregate material specifications in order to tailor aggregate use to the needs and available supply in their particular locations. Aggregate which account for 60 to 70 % of the total volume of concrete, are divided into two distinct categories-fines & course. Fine aggregate generally consist of natural sand or crushed stone with most particles passing through a 3/8 –in (9.5mm) sieve. Coarse aggregate are any particle greater then .19 in.(4.75mm), but generally range between 3/8 to 1.5 inches (9.5mm to 37.5mm) in diameter, Gravels constitute the majority of coarse aggregate used in concrete with crushed stone making up most of the reminder.
2.3.1 Physical Properties of Aggregate
1. Unit weight and voids
2. Specific gravity
3. Particle shape and surface texture
4. Absorption and surface moisture
2.3.2 Sand
Sand is an engineering material in concrete work. It is usually termed as fine aggregate. Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide, or SiO2), usually in the form of quartz.
General conditions of aggregate:
§ More or less 75% volume of concrete is aggregate. So good quality of aggregate should be used.
§ Aggregate act as filler materials on concrete.
§ Good quality of aggregate needed to make good quality if concrete.
§ Sand should be free from dust (Clay & silt).
§ Sand should be free from related silica or carbonate and organic matter
§ Sand should be well graded.
§ Washing of sand is necessary to remove dust,
§ Dust: This passes through the #100 sieve. (Dust= clay & silt).
2.3.2.2 Classification of Sand
According to the source
§ Pit sand
§ River sand
§ Sea sand
According to the Shape
§ Angular
§ Round
§ Flaky
According to the size
§ Coarse sand (3/8”), F.M-2.6
§ Medium sand (1/8”), F.M-2.2
§ Fine sand (1/16”), F.M- 1.8~2.0
2.3.2.3 Bulking of Sand
In the increase in the volume of a given weight of sand due to the presence of moisture, for up to about 5~8% of moisture of sand there is a steady increase in volume to about 20~30%.
The bulking of sand for small moisture content is due to the formation of the film of water around the sand grains and interlocking the air in between the sand grains and the film of water.
2.3.2.4 Particle Shape and Surface Texture
Rough texture, angular, elongated particles require more water to produce workable concrete then do smooth, rounded, compact aggregates. Aggregate should be relatively free of flat and elongated particle (Limit to 15% by weight of total aggregate). Important for coarse and crushed fine aggregate – these require an increase in mixing water and may affect the strength of the concrete, if cement water ratio is not maintained.
2.3.2.5 Sieve Analysis
A sieve analysis (or gradation test) is a practice or procedure used (commonly used in civil engineering) to assess the particle size distribution (also called gradation) of a granular material.
The size distribution is often of critical importance to the way the material performs in use. A sieve analysis can be performed on any type of non-organic or organic granular materials including sands, crushed rock, clays, granite, feldspars, coal, and soil, a wide range of manufactured powders, grain and seeds, down to a minimum size depending on the exact method. Being such a simple technique of particle sizing, it is probably the most common.
The results are presented in a graph of percent passing versus the sieve size. On the graph, the sieve size scale is logarithmic. To find the percent of aggregate passing through each sieve, first find the percent retained in each sieve. To do so, the following equation is used,
The next step is to find the cumulative percent of aggregate retained in each sieve. To do so, add up the total amount of aggregate that is retained in each sieve and the amount in the previous sieves. The cumulative percent passing of the aggregate is found by subtracting the percent retained from 100%.
% Cumulative Passing = 100% – % Cumulative Retained.
The values are then plotted on a graph with cumulative percent passing on the y-axis and logarithmic sieve size on the x-axis
Types of Gradation
Dense Gradation: A dense gradation refers to a sample that is approximately of equal amounts of various sizes of aggregate. By having a dense gradation, most of the air voids between the materials are filled with particles. A dense gradation will result in an even curve on the gradation graph.
Narrow Gradation: Also known as uniform gradation, a narrow gradation is a sample that has aggregate of approximately the same size. The curve on the gradation graph is very steep, and occupies a small range of the aggregate.
Gap Gradation: A gap gradation refers to a sample with very little aggregate in the medium size range. This results in only coarse and fine aggregate. The curve is horizontal in the medium size range on the gradation graph.
Open Gradation: An open gradation refers an aggregate sample with very little fine aggregate particles. This results in many air voids, because there are no fine particles to fill them. On the gradation graph, it appears as a curve that is horizontal in the small size range.
Rich Gradation: A rich gradation refers to a sample of aggregate with a high proportion of particles of small sizes.
2.4 Water
Potable water (That which is fit for human consumption) can be used without testing. This information summarized requirements for mixing water for use in ready mixed concrete. In October 2004, ASTM approved two new standards that address mixing water for use in concrete. While the requirements for water were addressed in ASTM C 94, increased pressure on concrete producers to use process water from concrete production operations and other recycled sources created a need for a more comprehensive coverage on standard of water.
2.5 Admixture
2.5.1 General
It is defined as a material other than water, aggregate and cement that is used as an ingredient of concrete to modify the properties of fresh or hardened concrete. Chemical admixtures are the ingredients in concrete other than Portland cement, water, and aggregate that is added to the mix immediately before or during mixing. Producers use admixtures primarily to reduce the cost of concrete construction; to modify the properties of hardened concrete; to ensure the quality of concrete during mixing, transporting, placing, and curing; and to overcome certain emergencies during concrete operations. Successful use of admixtures depends on the use of appropriate methods of batching and concreting. Most admixtures are supplied in ready-to-use liquid form and are added to the concrete at the plant or at the jobsite. Certain admixtures such as pigments, expansive agents, and pumping aids are used only in extremely small amounts and are usually batched by hand from pre-measured containers. The effectiveness of an admixture depends on several factors including type and amount of cement, water content, mixing time, slump, and temperatures of the concrete and air. Sometimes, effects similar to those achieved through the addition of admixtures can be achieved by altering the concrete mixture-reducing the water-cement ratio, adding additional cement, using a different type of cement, or changing the aggregate and aggregate gradation.
2.5.2 Use of Admixture
- Placing and finishing qualities
- Workability
- Strength development
- Appearance (gets improved)
2.5.3 Categories of Admixtures
- Water reducing admixtures,
- Retarding admixtures
- Air-entraining agents (AEA)
- Accelerating admixtures
2.6 Slump Test
The concrete slump test is used for the measurement of a property of fresh concrete. The test is an empirical test that measures the workability of fresh concrete. More specifically, it measures consistency between batches. The test is popular due to the simplicity of apparatus used and simple procedure. The slump test is used to ensure uniformity for different batches of similar concrete under field conditions, and to ascertain the effects of plasticizers on their introduction. The slump test result is a measure of the behavior of a compacted inverted cone of concrete under the action of gravity. It measures the consistency or the wetness of concrete. The slumped concrete takes various shapes, and according to the profile of slumped concrete, the slump is termed as true slump, shear slump or collapse slump. If a shear or collapse, slump is achieved, a fresh sample should be taken and the test repeated. A collapse slump is an indication of too wet a mix. Only a true slump is of any use in the test. A collapse slump will generally mean that the mix is too wet or that it is a high workability mix, for which slump test is not appropriate. Very dry mixes; having slump 0 – 25 mm are used in road making, low workability mixes; having slump 10 – 40 mm are used for foundations with light reinforcement, medium workability mixes having slump 50 – 90 for normal reinforced concrete placed with vibration, high workability concrete, slump > 100 mm.
The slump test is suitable for slumps of medium to high workability, slump in the range of 25 – 125 mm; the test fails to determine the difference in workability in stiff
Mixes, which have zero slumps, or for wet mixes that give a collapse slump. It is limited to concrete formed of aggregates of less than 38 mm
2.7 Setting of Concrete
Setting of concrete is defined as the onset of rigidity in fresh concrete. It is destined from hardening, while it describes the development of useful and measurable strength. Settings precede hardening, but it should be emphasized that both are gradual changes, which are controlled by the continuing hydration of the cement. Setting is a transitional period between states of the true fluidity and true rigidity. The penetration test according to ASTM C 403 is used to determine the initial and final setting of concrete. This test method covers the determination of the time of setting of concrete with slump greater than zero, by means of penetration resistance measurements on mortar sieved from the concrete mix. The penetration tests do not correspond to any specific change in concrete properties, although it is useful to consider that the initial set represents approximately the time at which fresh concrete can no longer be properly handled and placed, while final set approximates the time at which the hardening begins. Fresh concrete will have lost measurable slump prior to initial set, while measurable strength will be achieved sometime after final set. As per ASTM C403, the time of initial setting is the elapsed time, after initial contact of cement and water, required for the mortar sieved from the concrete to reach a penetration resistance of 3.5 Mpa (500 psi). Time of final setting is defined, in ASTM C 403, as the elapsed time, after initial contact of cement and water, required for the mortar sieved from the concrete to reach a penetration resistance of 27.6 Mpa (4000 psi).
2.8 Curing of Concrete
Adding water to Portland cement to form the water-cement paste that holds concrete together starts a chemical reaction that makes the paste into a bonding agent. This reaction, called hydration, produces a stone-like substance—the hardened cement paste. Both the rate and degree of hydration, and the resulting strength of the final concrete, depend on the curing process that follows placing and consolidating the plastic concrete. Hydration continues indefinitely at a decreasing rate as long as the mixture contains water and the temperature conditions are favorable. Once the water is removed, hydration ceases and cannot be restarted. Curing is the period of time from consolidation to the point where the concrete reaches its design strength. During this period, you must take certain steps to keep the concrete moist and as near 73°F as practical. The properties of concrete, such as freeze and thaw resistance, strength, water tightness, wear resistance, and volume stability, cure or improve with age as long as you maintain the moisture and temperature conditions favorable to continued hydration. The length of time that you must protect concrete against moisture loss depends on the type of cement used, mix proportions, required strength, size and shape of the concrete mass, weather, and future exposure conditions. The period can vary from a few days to a month or longer. For most structural use, the curing period for cast-in-place concrete is usually 3 days to 2 weeks. This period depends on such conditions as temperature, cement type, mix proportions, and so forth.
2.8.1 Curing Methods
Methods that supply additional moisture include sprinkling and wet covers. Both these methods add moisture to the concrete surface during the early hardening or curing period. They also provide some cooling through evaporation.
| v | Advantage | Disadvantages |
| Sprinkling with water or Covering with Burlap | Excellent results if kept constantly wet | Likelihood of drying between sprinklings; difficult on vertical walls |
| Straw | Insulator in winter | Can dry out, blow away, or burn |
| Moist Earth | Cheap but messy | Stains concrete; can dry out; removal problem |
| Pending on Flat Surfaces | Excellent results, maintains uniform temperature | Requires considerable labor; un- desirable in freezing weather |
| Curing Compounds | Easy to apply and inexpensive | Sprayer needed; inadequate coverage allows drying out; film can be broken or tracked off before curing is completed; unless pigmented, can allow concrete to get too hot. |
| Waterproof Paper | Excellent protection, prevents drying | Heavy cost can be excessive; must be kept in rolls; storage and handling problem |
| Plastic Film | Absolutely watertight, excellent protection. Light and easy to handle | Should be pigmented for heat protection; requires reasonable care and tears must be patched; must be weighed down to prevent blowing away |
2.9 Compressive Strength
Compressive strength is the capacity of a material or structure to withstand axially directed pushing forces. When the limit of compressive strength is reached, materials are crushed. Concrete can be made to have high compressive strength; many concrete structures have compressive strengths in excess of 50 MPa, whereas a material such as soft sandstone may have a compressive strength as low as 5 or 10 MPa. Compressive strength is often measured on a universal testing machine; these range from very small tabletop systems to ones with over 53 MN capacity. Measurements of compressive strength are affected by the specific test method and conditions of measurement. Compressive strengths are usually reported in relationship to a specific technical standard that may, or may not, relate to end-use performance
When a specimen of material is loaded in such a way that it extends it is said to be in tension. On the other hand if the material compresses and shortens it is said to be in compression. On an atomic level, the molecules or atoms are forced apart when in tension whereas in compression they are forced together. Since atoms in solids always try to find an equilibrium position and distance between other atoms forces, arise throughout the entire material, which oppose both tension and compression.
Finite strain theory, also called large strain theory, large deformation theory, deals with deformations in which both rotations and strains are arbitrarily large. In this case, the un-deformed and deformed configurations of the continuum are significantly different and a clear distinction has to be made between them. This is commonly the case with plastically deforming materials and other fluids and biological soft tissue. Infinitesimal strain theory, also called small strain theory, small deformation theory, small displacement theory, or small displacement-gradient theory where strains and rotations are both small. In this case, the un-deformed and deformed configurations of the body can be assumed identical. The infinitesimal strain theory is used in the analysis of deformations of materials exhibiting <href=”#Elastic_deformation” title=”Deformation (engineering)”>elastic behavior, such as materials found in mechanical and civil engineering applications, e.g. concrete and steel.
Large-displacement or large-rotation theory, which assumes small strains but large rotations and displacements. In each of these theories, the strain is then defined differently. The engineering strain is the most common definition applied to materials used in mechanical and structural engineering, which are subjected to very small deformations. On the other hand, for some materials, e.g. elastomers and polymers, subjected to large deformations, the engineering definition of strain is not applicable, e.g. typical engineering strains greater than 1%, thus other more complex definitions of strain are required, such as stretch, logarithmic strain, Green strain, and Almansi strain. The compressive strength of a material is that value of uniaxial compressive stress reached when the material fails completely. The compressive strength is usually obtained experimentally by means of a compressive test. The apparatus used for this experiment is the same as that used in a tensile test. However, rather than applying a uniaxial tensile load, a uniaxial compressive load is applied. As can be imagined, the specimen (usually cylindrical) is shortened as well as spread laterally. A Stress–strain curve is plotted by the instrument.
2.10 Strain
A strain is a normalized measure of deformation representing the displacement between particles in the body relative to a reference length. Strain is related to change in dimensions and shape of a material. The most elementary definition of strain is when the deformation is along one axis: Strain ??Change in length / Original length.
Strain, ?
Fig- 2.1 : Typical Stress Strain Diagram
It is found experimentally that an axial tensile loading induces a lateral strain corresponding to a reduction in a material specimen’s cross-sectional area. Similarly, an axial compressive load causes a lateral strain associated with an increase in the cross-sectional area. When the axial stress is removed, the lateral strain disappears along with the axial strain.
Fig- 2.2 : Typical Stress Strain Diagram
Strain is thus, a measure of the deformation of the material and is a non-dimensional Quantity i.e. it has no units. It is simply a ratio of two quantities with the same unit.
Normal strain: The amount of stretch or compression along a material line elements or fibers is the normal strain. If there is an increase in length of the material line, the normal strain is called tensile strain; otherwise, if there is reduction or compression in the length of the material line, it is called compressive strain. Normal strain is expressed as the ratio of total deformation to the initial dimension of the material body in which the forces are being applied. The engineering normal strain or engineering extensional strain or nominal strain e of a material line element or fiber axially loaded is expressed as the change in length ?L per unit of the original length L of the line element or fibers. The normal strain is positive if the material fibers are stretched or negative if they are compressed.
Shear strain: Strains which involve no length changes but which do change angles are known as shear strains.
= F / A?
Where,
?-Strain, E – Modulus of elasticity of Concrete, A= Cross Sectional Area, F= Applied Force / load. ƒ= Allowable strain in concrete.
EXPERIMENTS ON DEMOLISHED CONCRETE
3.1 Introduction
The compressive strength analysis will give the clear concept about the selection of aggregate before construction. Before the compressive strength test the below mentioned physical test have to perform.
3.2 Physical Tests
Physical tests for coarse aggregate
Sieve analysis
Abrasion test
Specific gravity and absorption capacity &
Unit weight & voids calculation.
Physical tests for fine aggregate:
Sieve analysis
Specific gravity &
Unit weight & voids calculation.
3.3 Coarse Aggregates Investigation And Preparation
Recycled concrete blocks were collected from demolished building. Then the Blocks were crashed manually. All the aggregates were washed properly to avoid dust and other impurities. Coarse aggregates sieved by the ASTM C 33-39 standards for the aggregate size of 20mm to 5mm (3/4 inch to 3/16 inch). Four sieves were used and they are 25mm, 20mm, 10mm and 5mm (1, ¾, 3/8, 3/16 inch). Aggregates had been taken in different sieved sizes. Saturated surface dried condition RCA used for concrete casting.
3.4 Sieve Analysis
This experiment is done to find the fineness modulus of coarse aggregate .sieve grading is given in the below table, In 3/4” aggregate –Maximum ¾” aggregate will be 10% of total aggregate.
Table 3.1: Recycled Coarse Aggregate case details
| Sl. No. | Case | Details |
| 1 | RBAY44 | Recycle Brick Aggregate 44 Years Old |
| 2 | RBAY40 | Recycle Brick Aggregate 40 Years Old |
| 3 | RBAY37 | Recycle Brick Aggregate 37 Years Old |
| 4 | RBAY35 | Recycle Brick Aggregate 35 Years Old |
| 5 | RBAY15 | Recycle Brick Aggregate 15 Years Old |
Table 3.2 Aggregate Percentage
| Sieve Size | Percentage Retained |
| 25mm passing 20mm retained | 4.97 % |
| 20mm passing 10mm retained | 57.53 % |
| 10mm passing 5mm retained | 37.50 % |
Table 3.3 The sieve analysis for 15 years old coarse aggregate (Sample quantity – 3000gm)
| Sieve Number | Sieve opening(mm) | Materials retained (gm) | % Materials retained | Cumulative % retained | Percent finer |
| 0.75 in. | 19.50 | 200 | 6.67 | 6.67 | 93.50 |
| 0.50 in. | 12.50 | 2075 | 69.17 | 75.84 | 24.16 |
| 0.375 in. | 9.50 | 567 | 18.9 | 94.74 | 5.26 |
| # 4 | 4.75 | 100 | 3.33 | 98.07 | 1.93 |
| # 8 | 2.36 | 20 | 0.67 | 98.74 | 1.26 |
| # 16 | 1.19 | 15.50 | 0.52 | 99.26 | 0.74 |
| # 30 | 0.59 | 12 | 0.40 | 99.66 | 0.344 |
| # 50 | 0.30 | 6.50 | 0.22 | 99.88 | 0.12 |
| # 100 | 0.15 | 1.60 | 0.05 | 99.93 | 0.07 |
| Pan | 2.40 | 0.08 |
Figure 3.1 Percent Finer vs Sieve Opening.
Table 3.4 Summary of Fineness Modulus Value
| Sl no | Type of sample | Fineness modulus | Average F.M |
| 1 | 15 years old coarse aggregate | 7.734 | 7.71 |
| 2 | 35 years old coarse aggregate | 7.728 | |
| 3 | 37 years old coarse aggregate | 7.676 | |
| 4 | 40 years old coarse aggregate | 7.69 | |
| 5 | 44 years old coarse aggregate | 7.715 |
3.5 Abrasion Test
Abrasion test is very important for coarse aggregate. There are four grading in abrasion test
Grade-A for > ¾” Aggregate – used in road construction
Grade-B for < ¾” Aggregate – used in building, bridge etc. construction
Grade-C for < ½” Aggregate
Grade-D for > ½” Aggregate
For our test it required B category aggregate in which 19.5mm pass and 12.5mm retained aggregate will be 2500gm and 12.5mm pass and 9.5mm retained aggregate will be 2500gm. It has to use 11nos of steel ball.
Table 3.5 Abrasion Test for 15 yrs Old Coarse Aggregate.
| Sieve size Passing (mm) | Sieve size Retained (mm) | Wt. of materials W1 (gm) | Grading of materials | No. of steel balls used | Wt. retained on one sieve, W2(gm) | Total wear W2-W1 (gm) |
| 19.30 | 12.50 | 2500 | B | 11 | 3080 | 1920 |
| 12.50 | 9.50 | 2500 | ||||
| Total weight, W (gm) | 5000 | |||||
Abrasion value =100 X (Total weight-W2) / W
= 100*(W-W2) / W
= 100* 1920 / 5000
= 38.40 %
Table 3.6 Summary of Abrasion Value
| Sl no | Agg. Age | Total weight (gm) | Total Wear (gm) | % Abrasion value |
| 1 | 15 yrs | 5000.00 | 1920.00 | 38.40 |
| 2 | 35 yrs | 5000.00 | 1965.00 | 39.30 |
| 3 | 37 yrs | 5000.00 | 1974.00 | 39.48 |
| 4 | 40 yrs | 5000.00 | 2070.00 | 41.40 |
| 5 | 44 yrs | 5000.00 | 2160.00 | 43.20 |
Note : For Fresh brick aggregate it found 37.34 %
Table 3.7 Specific Gravity and Absorption Capacity
| Wt. of Basket in Air (gm) | Wt. of Basket in Water (gm) | Wt. of SSD Sample (gm), B | Wt. of SSD Sample in water, C | Oven dry Wt. os Sample, A |
| 340.60 | 290.00 | 1000.00 | 540.00 | 885.00 |
Results
Bulk Specific Gravity (SSD Basis) = B/(B-C) = 1000/ (1000-540) = 2.17
Absorption Capacity, D% = {(B-A)*100}/ A = 12.99
Table 3.8 Summary of Bulk Specific Gravity & Absorption Capacity.
| Sl. No | Aggr. Age | Bulk Specific Gravity | Absorption Capacity |
| 1 | 15 years old | 2.17 | 12.99 |
| 2 | 35 years old | 2.20 | 10.86 |
| 3 | 37 years old | 2.20 | 11.86 |
| 4 | 40 years old | 2.15 | 13.25 |
| 5 | 44 years old | 2.13 | 14.94 |
3.6 Unit weight & Voids Calculation
Unit Weight test of the coarse aggregate were done according to the ASTM standard requirements of specification C29. Results of unit weight of RCA summarized.
Table 3.9 Summary of Unit Weight
| Sl. No | Concrete Age | Unit weight (Kg/m3) |
| 1 | 15 years old | 1161.53 |
| 2 | 35 years old | 1097.17 |
| 3 | 37 years old | 1089.90 |
| 4 | 40 years old | 1076.00 |
| 5 | 44 years old | 1097.89 |
3.7 Fine Aggregates
Sand was collected from the local market. Before using this sand, it had been washed properly to avoid mud and other organic materials. All sand sieving through No 4 sieve. ASTM sieve to ensure that no big particle or no rubbish ware present into it. After washing the sand, it had been dried in the laboratory and then SSD (Saturated surface dry) was prepared. Sand had been putted into the plum and then pressed, while it tends to congregate, then it was assumed that sand was in SSD condition. After prepared the sand, it had been putted into air tied bags to avoid moisture.
Table 3.10 The Sieve Analysis for Fine Aggregate (Sample quantity – 500gm)
| Sieve Number | Sieve opening(mm) | Materials retained (gm) | % Materials retained | Cumulative % retained | Percent finer |
| # 4 | 4.75 | 0.00 | 0 | 0 | 100 |
| # 8 | 2.36 | 15.80 | 3.16 | 3.16 | 96.84 |
| # 16 | 1.19 | 96.80 | 19.36 | 22.52 | 77.48 |
| # 30 | 0.59 | 183.80 | 36.76 | 59.28 | 40.72 |
| # 50 | 0.30 | 133.90 | 26.78 | 86.06 | 13.94 |
| # 100 | 0.15 | 59.70 | 11.94 | 98.00 | 2 |
| Pan | 10.00 | 2.00 |
Fineness Modulus (F.M) = (Sum of Cumulative %Retained / 100) X 100 = 2.69
Graph 3.2 Percent Finer vs. Sieve Opening.
3.9.1 Specific Gravity of Fine Aggregate
| Sl no. | Wt. of OD sand (gm) A | Wt. of Pycnometer + Water (gm) B | Wt. of Pycnometer + Water + sand (gm) C | Wt. of SSD sand (gm) S | Bulk sp. Gr. (SSD) | Avg. Bulk sp. Gr. (SSD) | Bulk sp. Gr. (OD) | Avg. Bulk sp. Gr. (OD) | App. Sp. Gr. | Avg. App. Sp. Gr. (OD) | Absorption (%) | Avg. Absorption (%) |
| 1 | 351.80 | 1227.60 | 1449.00 | 365.80 | 2.53 | 2.44 | 2.7 | 3.98 | ||||
| 2 | 500.00 | 1246.40 | 1560.20 | 509.20 | 2.61 | 2.57 | 2.55 | 2.50 | 2.69 | 2.70 | 1.84 | 2.94 |
| 3 | 398.20 | 1197.80 | 1446.00 | 410.20 | 2.58 | 2.5 | 2.71 | 3.01 |
Sample Calculation:
Bulk Specific Gravity (Oven dry basis),Sd, 23/23°c
= A/(B+S-C) = 351.80 / (1227.60 + 365.80 – 1449.00) = 2.44
Bulk Specific Gravity (Standard surface dry basis),Ss, 23/23°c
= S/(B+S-C) = 365.80 / (1227.60 + 365.80 – 1449.00) = 2.53
Apparent Specific Gravity,Sa, 23/23°c
= A/(B+A-C) = 351.80 / (1227.60 + 351.80 – 1449.00) = 2.70
3.8 Cement
Cement collected from the local market and its initial setting time and final setting time were 115 and 183 minutes respectively. The unit weight of the cement was approximately 3100 kg/m3.
3.9 Water
Water that was used in the concrete mixing and the curing of the specimens was normal tap water which unit weight was 1000 kg/m3 (Approximately).In general, the air percent of the mix design was assumed as 2%. The cement content of the ratio was for the workability of the concrete.
Table 3.11 Mix Proportion for Concrete (Weight Basis)
| Sl. No. | Case | Cement (kg) | Water(kg) | Adm.(ml) | Sand (kg) | Aggregate (kg) |
| 1 | RBAY44WC55 | 1.93 | 1.05 | 4.45 | 4.48 | |
| 2 | RBAY44WC50 | 1.93 | 0.95 | 4.56 | 5.59 | |
| 3 | RBAY44WC45 | 1.93 | 0.85 | 17.41 | 4.67 | 4.72 |
| 4 | RBAY40WC55 | 1.93 | 1.05 | 4.45 | 4.48 | |
| 5 | RBAY40WC50 | 1.93 | 0.95 | 4.56 | 4.59 | |
| 6 | RBAY40WC45 | 1.93 | 0.85 | 17.41 | 4.67 | 4.72 |
| 7 | RBAY37WC55 | 3.22 | 1.74 | 7.41 | 7.47 | |
| 8 | RBAY37WC45 | 3.22 | 1.42 | 29.01 | 7.78 | 7.84 |
| 9 | RBAY35WC55 | 3.22 | 1.72 | 7.41 | 7.47 | |
| 10 | RBAY35WC45 | 3.22 | 1.42 | 29.01 | 7.78 | 7.84 |
| 11 | RBAY15WC55 | 3.22 | 1.74 | 7.41 | 7.47 | |
| 12 | RBAY15WC45 | 3.22 | 1.42 | 29.01 | 7.78 | 7.84 |
3.10 Mold Preparation
Mold cylinder was the 4 inch on diameter and 8 inch in height. The entire molds were prepared properly before putting the concrete into these. Molds were bringing lubricated inside before casting of concrete specimens.
3.11 Casting
Concrete prepared by using mixture machine. Trial mix was done for every case before the final mix. However, the mixing procedure was quite different from the normal mixing in Bangladesh. In Bangladesh, all the element, such as cement, sand and water put together in the mixture machine and then aggregate was placed inside it. But in fact, it is not a good way to gain the good strength of the concrete. To ensure the quality strength in the matrix, the following format was followed for mixing concrete.
At first put ½ of the sand in the mixing machine and then spread it the mixing machine; then put fall cement and after then put other ½ sand in the machine. Than mix these for 60 second to get a uniform mixture. After that, put water gradually into the mixing machine and mix these for 60 second. After that, add the coarse aggregate into the machine and mix for the 180 seconds, after producing the mix concrete, slump test were always done and after slump test, casting was done of the specimens.
For water-cement ratio 0.45, 0.50 & 0.55, high-range water reducing chemical admixture was mixed with water at the time of casting in case of w/c ratio 0.45.
3.12 Compaction of the Concrete
Concrete of the specimens had been properly compacted. Each and every cylindrical and cubic specimen was compacted by three layers. In each layer, there were 25 blows. After the compaction of these specimens, scaling and hammering were done to get a void free surface of the specimens.
3.13 Curing of Concrete
Curing of the specimens was completely ensured after the casting. Normal tape water was used for the curing procedure. Specimens kept under water in a water drum. Before crashing of those specimens, all the specimens were places into the water tank for under water curing and the duration were 28 days.
3.14 Destructive Test by Universal Testing Machine
The Universal Testing Machine had used to do destructive tests for all the concrete specimens. Before the destructive test of the cylindrical specimens, capping was done over those specimens to get uniform and smooth surface for concentrated loading. Loading was 4KN/sec applied by the Universal Testing Machine over the specimens. Stress Strain was measured for each case. Crashing pattern and crack surface picture were taken for the specimens. Concrete used for residential purposes is around 2,500 psi (17 MPa), around 4,000 psi (28 MPa) for commercial uses, and as high as 10,000 (70 MPa) for other specified applications. Strains were measured by strain gauge. Allowable strain of 0.003 in./in adopted by the ACI as a safe limit value.
Compressive Strength with Stress Strain Graph for (15yrs old aggr., w/c-0.45, 28 days)
| Sample – 1 | Sample – 2 | Sample – 3 | |
| Diameter (in.) | 4 | 4 | 4 |
| Diameter (m.) | 0.106 | 0.101 | 0.101 |
| Crushing Load (KN) | 182 | 185 | 187 |
| Area (m2) | 0.008 | 0.008 | 0.008 |
| Stress (MPa) | 22.434 | 22.434 | 22.434 |
| Stress (Psi) | 3253.416 | 3253.416 | 3253.416 |
Table 3.12 Dial Reading
| Load (KN) | Sample-1 | Sample-2 | Sample-3 |
| 0 | 0.000 | 0.000 | 0.000 |
| 10 | 0.000 | 0.000 | 0.000 |
| 20 | 0.010 | 0.005 | 0.010 |
| 30 | 0.030 | 0.010 | 0.015 |
| 40 | 0.050 | 0.025 | 0.019 |
| 50 | 0.060 | 0.030 | 0.025 |
| 60 | 0.070 | 0.040 | 0.050 |
| 70 | 0.080 | 0.045 | 0.060 |
| 80 | 0.090 | 0.050 | 0.070 |
| 90 | 0.095 | 0.055 | 0.075 |
| 100 | 0.105 | 0.065 | 0.080 |
| 110 | 0.150 | 0.080 | 0.090 |
| 120 | 0.170 | 0.090 | 0.095 |
| 130 | 0.180 | 0.100 | 0.100 |
| 140 | 0.190 | 0.110 | 0.225 |
| 150 | 0.210 | 0.140 | 0.350 |
| 160 | 0.250 | 0.180 | 0.465 |
| 170 | 0.300 | 0.220 | 0.585 |
| 180 | 0.075 | 0.400 | 0.750 |
| Crushing Load | 182.00 | 185.00 | 187.00 |