COMPRESSIVE STRENGTH EFFECTS OF WASTE PLASTICS, GLASS AND DEMOLISHED CONCRETE AS PARTIAL REPLACEMENT FOR AGGREGATES IN CONCRETE MIX
Concrete is a stone like materials obtain by designing a carefully proportioned mixer of cement, sand and gravel or other aggregates and water to harden in forms of shape and dimensions of desired structure. Sand is one of the main constituents of concrete; it acts as filler in concrete. Concrete is most widely used man made construction materials and its demand is increasing day by day. Concrete, being the vital and usually used material, is called upon to acquire very high strength and ample workability properties. Concrete is the most inevitable and requisite material used in infrastructure improvement throughout the globe. (Sameer Shaikh et al., 2015).
According to Portland Cement Association (PCA), “the primary difference between high-strength concrete and normal-strength concrete relates to the compressive strength that refers to the maximum resistance of a concrete sample to applied pressure. Although there is no precise point of separation between high-strength concrete and normal-strength concrete, the American Concrete Institute (ACI) defines high-strength concrete as concrete with a compressive strength greater than 6,000 psi”.
A modern lifestyle, alongside the advancement of technology has led to an increase in the amount and type of waste being generated, leading to a waste disposal crisis. Following the normal growth in population, the amount and type of waste materials have increased accordingly. Many of the non-decaying waste materials will remain in the environment for hundreds, perhaps thousands of years. These waste materials nowadays are major problem, which is a threat to the environment. This is one of the problems that are encountered in the Philippines each year. Most of these materials are left as stockpiles, landfill materials or illegally dumped in selected areas. The practice of possible recycling waste materials helps in reducing detrimental environmental impacts of the construction industry. Environmental pollution is the main hazard faced today. Dumping of wastes will cause pollution to the environment.
Thus, researchers have begun investigating the potential of these materials in eco-friendly way. It is very important to reuse and disposed these materials. Such recycling not only helps conserve natural resources, but also helps solve a growing waste disposal crisis. There are many ways that waste will be used; the best example is in the construction works. Examples of these waste materials are waste plastics, waste glass and demolished (pervious) concrete that are generally common waste that can be seen in our environment. In order to lessen the waste materials that are everywhere, this study will be conducted to reuse and recycle waste products in the field of construction.
OBJECTIVE OF THE PROBLEM
This study aims to determine the performance and compressive strength of waste plastic, glass and demolished (pervious) concrete as partial replacement of aggregates in concrete mix. Specifically, it seeks to answer the following questions:
Is it feasible to combine the 3 materials (waste plastic, glass and demolished/pervious concrete) as partial replacement of aggregates in concrete design mix?
Does using waste plastic, glass and demolished (pervious) concrete as partial replacement of aggregates in the concrete mix affect the workability and strength of the construction material?
Does it assess if the samples will achieve a standard concrete with a compressive strength of not less than 3000 psi using the alternative 3 selected waste materials in concrete?
Can all of these selected waste materials be used as an alternative aggregates in concrete in light of the rising costs of construction materials?
SIGIFICANCE OF THE STUDY
This study provides an additional and innovative uses of waste materials as substitute replacement for aggregates in making concretes. Thus, recycling and reusing these waste materials as aggregates could offer a solution to the problems encountered with the quarrying of natural aggregates and disposal of old concretes. In addition, this study is an essential step towards promoting a sustainable safe and economic disposal of solid wastes.
SCOPE AND LIMITATION OF THE STUDY
This study focuses on the effective percentage replacement and assessment if the sample can achieve compressive strength of 3000 psi by using waste plastic as partial replacement with waste glass as fine aggregates and demolished concrete as course aggregate. The materials were controlled by ordering from one supplier only. Accumulating all the materials the mixture of concrete contains the cement, water with desire combination percentage aggregates of 10%, 30% and 50%. There are five samples for each percent replacement including 0% replacement for a total of 20 samples. Samples for each mixture are subjected to curing. The two samples of each mixture are test on the UTM for its compressive strength on the 3rd, 7th, 14th, 21st, and 28th day.
REVIEW OF RELATED LITERATURE
A material that is widely used in building constructions consists of aggregates and sometimes admixtures in required proportions which are joined together by cement and water. The compressive strength, workability and other characteristic of concrete depends on the properties of its proportion mix, the properties of the aggregates and other mixtures and the method of compaction in order to obtain a Standard Concrete (Monteiro, et al., 2006). According to Portland Cement Association (PCA), “the primary difference between high-strength concrete and normal-strength concrete relates to the compressive strength that refers to the maximum resistance of a concrete sample to applied pressure. Although there is no precise point of separation between high-strength concrete and normal-strength concrete, the American Concrete Institute (ACI) defines high-strength concrete as concrete with a compressive strength greater than 6,000 psi”.
Concrete properties at early age
Early age properties are important because of the significant construction loads that a structure can be subjected to in the few days after the placement of concrete. They are also significant, as they affect long-term performance.
The concrete strength at seven days for standard concrete is approximately 75 percent of its 28-days strength. The boost in the strength with age is a nonstop process as long as any unhydrated cement still exists within the toughened concrete. It is therefore important that early-age characteristics as well understood so as to formulate the construction stages that have to be undertaken to satisfy the structural design load and deformation demand as stated by Nawy, 2011.
Type 1 of Portland cement can be used to obtain standard concrete mixtures with a compressive strength of 3000 psi. However, to obtain a higher compressive strength it is necessary to add chemical and mineral admixtures to the concrete. With the addition of mixtures, the cement-admixture compatibility becomes a key factor. According to Monteiro (2006), experience has shown that with naphthalene or melamine sulfonate type superplasticizer, low C2A and low-alkali Portland cements generally produce concrete mixtures which do not show high slump loss with time. Because of this, using a new generation of superplasticizers does not cause slump loss with almost all kinds of ordinary Portland or blended Portland cements, this superplasticizers are called polyacrylate copolymers.
Cement is not the only thing that makes a good concrete, aggregates are also essentials in making high quality concrete. Dhir (1976) specified that the aggregate costs more than the cement. This is very good reason why the importance of aggregates should be appreciated. Some people are apt to think that once they have bought good cement they can use almost anything with it to make concrete. Good aggregate not only helps to make good concrete, but results in lowering the cement content, thus giving a concrete which is actually cheaper per cubic yard than one made with an inferior aggregate. PCA indicated that when selecting aggregates for high-strength concrete, producers consider the strength of the aggregate, the optimum size of the aggregate, the bond between the cement paste and the aggregate, and the surface characteristics of the aggregate. Any of these properties could limit the ultimate strength of high-strength concrete.
Demolished Concrete, DC (Pavement)
Coarse demolished concrete (pavement) can be produced by crushing and demolishing waste not less than 95 percent by weight of concrete, and its total containment level should be at least lower than 1 percent of the bulk mass. The materials that can be found in DC are the usual mixtures of concrete or sometimes other admixtures that are combined with a typical which means that it is good for premix concrete production.
As described by CEMEX, “recycled concrete is created by breaking, removing, and crushing existing concrete to a preferred size. It is commonly used as a base layer for other construction materials because it compacts to form a firm surface.” Here in the Philippines, recycled concrete has been the most common construction and demolition waste used in concrete production both as coarse and fine aggregate. Recently, the availability of the recycled concrete in the country is about a million tons.
Most concrete structures are designed under assumptions that are concrete resists compressive stresses but not tensile stresses; hence for the purpose of structural design the compressive strength is the criterion of quality (Troxell, et al., 1968). This is because the compressive strength for the concrete is so much greater than tensile strength. Compressive strength is the maximum load per unit area sustained by a concrete specimen before failure in compression (Akroyd, 1962). The compression test is relatively easy to make, and cubes and cylinders are the common types of compression test specimens used to determine the compressive strength. The strength of concrete increased with respect to time and temperatures. A given strength may be achieved by keeping the concrete for a long time at a low temperature or a shorter time at higher temperature. The direct relationship f strength to maturity varies with the composition of the concrete and the type of quality of the cement (Akrotd, 1962).
A Universal Testing Machine (UTM) will be used to determine the characteristic strength of concrete. According to Olsen (2008), “UTM is a test of mechanical properties such as tensile flexural, compressive and shear are among the most commonly used instruments plastics compounders are likely to buy when outfitting a lab. Product development is among the key reasons compounders and resins makers test compounds and resin with UTM’s. Others include testing the materials to determine its suitability for various plastics processes and whether its properties will meet the particular end-use application, as well as for quality control following development to ensure lot-to-lot consistency”.
ACI mix design standard is use for normal concrete in computing the design mixture of the concrete. Furthermore, the amount of selected waste materials used is dependent on the computed weight cement and sand, respectively.
PREPARATION & COLLECTION OF SPECIMENS
The materials that will be used in this study include cement, fine and coarse aggregates and water. The cement that will be used is type 1 Portland cement. The fine aggregates that will be used are pulverized waste plastics with waste glass. Fine aggregates passed through sieve no. 4 (4.75 mm) and demolished concrete that will be used as the coarse aggregates. The size of the demolished concrete is ¾ in. Water is also used to serve as bonding agent to the mixture, thus water is clean and free from any deleterious materials.
The collection of the materials: the demolished concrete is taken from a concrete pavement. This recycled concrete is transported to a location to dump the waste of the reclamation of the pavement. The researchers are able to have 4 sacks of recycled concrete pavement from Don Carlos, dump for free. The desire compressive strength of this concrete is 3500 psi. This study aims to recycle the concrete pavement to reduce the wastes and to be able to use the waste as aggregates. The demolished concrete is crushed to a desire size of ¾ in to 1 in.
Alternative materials used in the study are the plastics and glass, waste that are commonly found in our environment nowadays. These materials help the concrete to increase the strength. The researchers are able to collect two bags, 1 bag for waste plastics and 1 bag for waste glass from Maramag, Bukidnon. It is economical than the usual aggregates.
The physical properties of selected waste materials: the properties are composed of fineness modulus, specific gravity, moisture content and absorption. For the sand, it has the properties of 2.65, 2.6, 6.5 and 2.5 respectively. For gravel, it has 2.7 of specific gravity, 3.5 of moisture content, 2.5 of absorption but it has fineness modulus. For demolished concrete, it has no fineness modulus also, 2.4 of specific gravity, 3.5 of moisture content and 5.7 of absorption. For waste plastics with waste glass, 2.8 – 3.36,
The crushing of demolished concrete: The collections of demolished concrete are in the form of blocks, in order to make it as an aggregate. The demolished concrete is crushed to desire size range ¾ in to 1 in. (puwede hammer ang gamiton but pwd sad equipment sa DPWH if nay available.)
The mixing and filling of concrete in molds: after batching process of the materials, the final materials are added in order to bind the materials with water. Water is added accordingly on the ACI mix design. Shovel is used to mix the materials then pour the mix materials into the molds. For the 1st layer, the mold is filled with 1/3 of its height with the mix and tampered 25 times. Tampering is done to prevent voids in concrete and the concrete is compact.
The compression test is done to determine the strength of the concrete. The compressive strength of each sample of different percentage replacement is test on its 3rd, 7th, 14th, 21st, and 28th day. The apparatus used is the Universal Testing Machine (UTM).
Collection of materials
The cement to be used for this study will be Portland cement type 1. The aggregate will waste plastics, glass and demolished concrete. The coarse aggregate (demolished concrete) will be crushed in a size of 34 inch. The water to be used in mixing is potable water.
Preparation of equipment
Experimental design and mix proportion
The ratio of the materials will be 1:2:4. For the aggregate, 10% of it will be grind plastics, 30% will the pulverized glass and 50% of the crushed demolished concrete. The design mix is by volume wherein there are 4kg of coarse aggregate in every 1kg of cement and 2kg of fine aggregate.
( Summary of mix proportion. )
The preparation of the pervious concrete specimens will be prepared in general accordance with ASTM C192, practice for making and curing concrete test Specimen in the laboratory (ASTM, 2014). The collected glass will be pulverized manually with the use of sack and hammer and undergo sieving passing US standard sieve no. 40, waste plastics will be grinded and the demolished concrete will be crush in a size of 34.
The mould to be used for casting the specimen is a cylinder with dimensions of 6 in diameter and 12 in in height. The prepared mixtures will be casted in the moulds and left to set for 24 ± 8 hours. Once the specimen is dry, it will be taken out from the moulds an subjected to curing for 28 days. Five specimen per mix proportion will be prepared.
(Testing of specimen)