It is believed that the use of recycled materials in the making of concrete started during the period of World War 2, these materials were used in the construction of base course for roads. The basic advantage of adopting these materials for constructional purposesis economic , other schools of thought give environmental reasons for the adoption of these materials in construction.The materials derived from construction sites come in large volumes and as time goes on they increase.To reduce the impact of these materials in the environment the construction industry has decided to adopt these materials in construction works.
Recycled aggregate can be obtained from the destruction of construction material which is generally made up of broken parts like brick walls and slabs.Since the nature and strength of these materials can not be ascertained,eg the ratio or proportion of cement to that water, and other parameters like the origin of the constituent aggregates and what went on within the material during its use, reference is only made to the historical data of the constituents. This has in the last few years fueled research in this area, as most construction industries want to know the probability of these materials providing the desired service if used in the construction of concrete products.
In view of obtaining an accurate result of a concrete beam through the usage of recycled aggregate, it is compulsory and advisable to make sure that the least and basic necessities are in place which must be in alliance or conform to the structural building standards or laws guiding the construction of concrete beams. The accepted composition of mix is the basic requirement which is used to determine the performance of concrete, therefore the mixture ratio and concrete manufacturing techniques are also vitally required (Moses, 2001). The aggregates to be recycled are basically composed of the initial materials and additives. The constituents of the aggregates which have been recycled rely and is dependent on the combined action of both the additives nature and quantity used, therefore, adequate measures or appropriate techniques or methodologies are been ensured so as to keep check or watch on the nature and quantity or amount been utilized in order to obtained the desired output. The additive used, which is normally a mortal which is adhered is porous in nature and as a result of these is highly dependent on the ratio or proportion of water to that of cement based on the proposition of recycled concrete applied.
By applying various methods or techniques that are employed in reducing the concrete materials into smaller pieces in order to obtain aggregates that are coarse in nature for construction purposes, of recent concrete is one of the procedures of obtaining an easy concrete in the physical setting of the work place. This minimizes or brings about a reasonable reduction, the involvement of the physical deposits and land needed for the concrete considered as reminants.
Concrete Aggregate Replacements
Alternative materials needed commonly regarded as components of the concrete aggregate comprises of sand (that is smooth particles) In which different sizes comprising of various patterns of coarse stones in form of gravel are used. Furthermore, there is an increasing and enthusiastic urge in applying these alternative apparatus in place of the original constituents in a wide and detailed range. In view of these, alternative materials limitation have not been placed on the usage of materials since there other vital research materials as indicated in a study by Moses (2001),
“that such granulated coal ash, lags of or various rigid remnants comprising of fiberglass remnants components ,plastics, which have been granulated, products consisting of wood and paper wastes, sludge sintered in pellets from a wide range of options, as a result of the availability or presence of these alternative materials, which can be efficiently and conveniently applied ”.(p.24)
Only two of the materials have been used, they include basically cullet of glasses and recycled concretes which have been crushed.
Despite the fact that aggregate normally to about 0%, 50%, and 100% of the concretes available quantity, is normally considered as filler which is noble in nature and has some degree of influence on the final and processed concrete constituents. Moreover, research has reviewed that the components of aggregate has been noticed and recommended to play a vital and significant role in obtaining the performance, mightiness, stability dimensional requirement, and the duration of the concrete constituents. Furthermore, aggregates can have a reasonable influence on the cost of the resultant mixture of the concrete.
Various data or parameters of the aggregate components have been reviewed to be vital in the field of engineering application, and as a result of this great importance been attached to the different data or parameters of the components of the aggregate, it’s been highly utilized in the analysis of concrete to review it’s toughness, mightiness and duration. As a result of the nature and type of materials required, provision should be made to ensure that components of the aggregate are neat and free from chemicals, coatings of clay ,including other smooth components or materials which are to be concentrated so that it can change the union of the paste of cement and it’s hydrated nature.
It’s vital to consider the distinction between cement and aggregate, this is because most of the materials found usage both as cementations components and as aggregates (for instance some slag’s of blast furnace). Constituent materials that have been sought for or used as substitutes of cement are discussed in another article of Inventory Technology-Substitutes of Cement.
Aggregates which comprises of concretes that are recycled broadly has a minimal specified gravity and a larger rate of absorption than the other alternative aggregate of gravel. After undergoing a serious and extensive research by various researchers in different schools of thought relating to this field under study, observations, results, and conclusions obtained by the different researchers when analyzed differently and collectively, shows that, concrete that is derived from recycled materials is as good as those that are made from direct materials; this also has to do with its resistance and its persistence ability to freeze-thaw in a dripping wet state.
The cognitive ability changes with its main concrete and water-cement proportion of the recent components of the concrete. It has also been observed that red concrete produced from materials that have been recycled has a good percentage of the cognitive ability of that which is obtained from construction materials naturally.
Components of glass usually serve as a crack arrestor, benefits of concrete duration, in as much as this relies greatly on the specific glass aggregate constituents; the concrete and its use at the end of research work still remain the same. Glass aggregate can permit a larger range of decorative options for concrete aggregate.
Most of the additional interest of engaging glass as an aggregate material in the concrete includes:
- concrete unit cost reduction
- minimizing of freight cost
- Exclusion of landfill concrete costs
The technique adopted in the breaking down of the material to be recycled has an impact which is direct on the final material that is obtained. The density and the ability of the material to be recycled to take in water or moisture are subjective to the adhered mortal, and cognition has to be taken of this before the adoption of the recycled material in production of what ever form of concrete. This knowledge will not only help the person utilizing the recycled material for the purpose of construction, but will go a long way and assist him to have a direct control over the characteristics of the final product rather than been dependent on others which on the other hand increases reliability reduces the duration. The ability of the recycled material to take in water or moisture is one of the most important characteristic that differentiate recycled materials from fresh or raw materials and the absorption ability has direct consequence on both the newly constructed concrete and the characteristics of the final concrete. Most experiments that are carried out on recycled sand materials are often time excluded; this is due to its ability to take in moisture, which it is discovered will have a shrinkage consequence.
If aggregates that are recycled applied in dry situations the concrete’s performance is largely minimized due to their holding ability. In a work by Yang, et al (2008),”he argue that the aggregates recycled should be saturated before been put into use
generally the performance of recycled aggregate concretes is influenced by the holding capacity of the recycled aggregates” (p.26). The nature of the aggregates can also influence the workability of the listed concretes,it’s dependency on the type of crusher employed. The aggregate components of recycled concrete compare well to alternative aggregates in that they contain fine particle shape, high holding capacity, and minimal specific gravity. Another important observation made with the use of recycled materials after undergoing a serious examinations on the materials is that the volume of the material used does not respond to changes in temperature and moisture intake.It is important to know that when gypsum is available in the materials are to be used for recycling, as it is presently practiced, certain reactions are bound to occur due to the presence of sulphate ions.. Benjamin (1998) stated that “the density of a beam that is cast using recycled materials shows an opposite make up with the natural concrete”(p.57). In this case the density of the final material or product obtained is less when making comparism with concrete made from normal materials.
It has been found that the performance of recycled concrete is minimum, This is as a result of the increase in the quantity of the recycled material in th concrete mixture. The values of other parameters such as toughness reduces to a large extent. The ability of the recycled material to resist frost is the same in proportion to that of concrete made from natural materials.
Yang. et al. (2008) premeditated on the breakdown possibility of recycled concrete beam and noticed that the failure of the concrete derives from its weakest point. The point at which failure is likely to occur in concrete with medium strength ability is found to be within the internal composition of the recycled materials themselves.
Benjamin, (1997) in his work stated that “the medium strength conventional concretes, the interface in the weakest point, however, this is not the case when the concrete is made with recycled aggregates, as what happened in high strength concretes where the failure is through the aggregates”(p.25).
Yang,et al. (2008,) “research work also shows splitting tensile failure of concrete made with a high amount of recycled aggregates. The failure happened through the recycled aggregates the recycled aggregates being the weakest point”(p.16). This gives rise to a couple of symmetric sides that look alike. Avaan (2007). Studied” the behavior of concrete beam made with conventional and recycled coarse aggregate, each specimen without shear reinforcement exhibited an initial flexural crack at the centre of the specimen and subsequent flexural cracks away from that section”(p.16). It was discovered that as load was added, one of the flexural crack increased and formed what is referred to as a diagonal crack close to one of the supports. It was also observed that after the diagonal crack occurred, another form of failure was found to occur which is referred to as brittle failure.
If splitting cracks are to be taken cognizance of along the tension reinforcement, especially in beams made of the materials that have been recycled (Gomez-Seberon, 2002). The involvement of the right amount of shear reinforcement reduced to the barest minimum this horizontal –splitting failure and as a result the reaction to shear was enhanced. Beams that are constructed with the use of recycled materials are discovered to posses the same amount of shear force when there is an occurrence of failure as beams that are made or produced from conventional materials which have the same quantity of transverse reinforcement. When the sum total of transverse reinforcement is enhanced and there is a reduction in the stirrup spacing, the observation is that the stirrup yield is enhanced. But if the transverse reinforcement is increased, which is done by enlarging the width of the stirrup, and maintaining the spacing, the resultant effect is that the shear force is increased. One of the main observations made at this point was that only the beams constructed with the use of recycled materials resulted to shear force at stirrup yield in the given intervals.
In a research by Moses,(2001), he stated that “the ratio of shear force at failure to shear force at cracking indicates that the recycled concrete beams reached shear force at cracking in earlier load stages than conventional concrete beams”(p.13).
Strength of Reinforced Beams Using Recycled Materials
The strength of a reinforced beam can be said to be the maximum amount of load the reinforced beam or concrete can hold. When concrete are left on their own with no external force applied they poses some great deal of strength or are said to be hard ,but at the introduction of tension the strength of the concrete is drastically reduced.
As a result of this observations, construction work made from concrete materials with the exception of making ways are made putting in mind the fact that concrete has no ability to withstand tension and thus reinforcement are constructed or made to carter for the tension. Improvements in technology and its use in construction , concrete materials are obtained with greater strength and adopted in construction work such as high rise buildings and other construction works. Also, the tensile and shear capability of concrete that has relatively high strength does not add in quantity with cognitive strength. Taking cognizance of the two basic properties of strength, the most important of the two is the shear strength. This is due to the fact that the tensile strength has little contribute when it comes to the ability of the concrete to carry load.
Some structural concrete are estimated to have strength of 20-30Nmm-2 at 28 days. Avaan, (2008 ) studied that “concrete made with 100% of recycled coarse aggregate with lower water-cement proportion than the conventional concrete can have larger compression strength”(p.17).
Compression which is transferred in reinforced concrete beams depends largely on the tensile and shear capability of the concrete materials. The compression in a boasted concrete beam without compressive reinforcement is carried along by a combination of three basic materials.
- Concrete in the shear zone.
- Dowelling action of tensile boasting.
In flexural components in specifically the compression interfering mechanism interacts vividly with the union existing between concrete and the embedded boasting and the anchorage of the reinforcement. Abraham(1998) in his studies was of the opinion that
“Considering the procedure in which the compressed strength of concrete advances with the shear ability, the ACI Building Code makes an assumption that the nominal compressive capacity (compressive ability of beam without shear boasting) is basically a function of the square root of the shear strength while the British Standard considered it as being directly proportional to the cube root of the shear capability”(p.17).
In most of the earlier mentioned codes, the compressive ability of a reinforced concrete component without shear reinforcement is computed by applying empirical methods which are based mainly on experimental outcomes obtained using simply aided beams(Abraham,1998).
They finalizes that through the applications of the recent ACI code formulae, the compressive ability of RAC can be estimated in excess.In view of trying to avoid this overestimation and to obtained a result that can give an accurate or at least an approximate and acceptable result,10 out of the 12 beams they reported were examined under a relatively minimal range to depth proportion ( 2.0), and hence can be regarded as beams of greater depth, an unlikely aim or objective for RAC usage.
Avaan (2008 ) discovered that “the compressive ability of concrete is dependent paramountly on the capability of the coarse aggregate materials to resist or have a reasonable percentage of persistence over the shearing stresses, the cube and cylinder shear abilities and the indirect compressive strength are embedded in the comparison, meaninn the RAC cube ability was 88.4% of that of the usual concrete”(p37).
Generally, there is a 10% reduction in ability when recycled coarse aggregates are applied. The vital distinction in strength decrement reveals the influence of the several factors such as the source of the recycled aggregate and reveals that the need to examine local components for the real characteristics (Moses,2001,p.5)
Strength of Recycled Aggregate Concrete
The mechanical components and the strength behavior of recycled aggregate concrete (RAC) must be observed in view of ensuring effective utilization of the recycled material. There have been various studies patterning with the mechanical and durability characteristics of RAC.
Benjamin (1997) suggested that the “formulae for the modulus of elasticity that give a mean reduction of 15% for NAC and RAC of similar cylinder shear abilities”(p.38).
RAC has been revealed to be weaker than a relative concrete composed of natural aggregate which could hence be softer as a result of the strain at highest stress could be wider than the typically assumption made on the value of 0.002 ( Yang,2008.pp5 ). Thus the modulus of elasticity and the strain at the highest stress of locally manufactured RAC required undergoing a study so to achieve the compulsory confidence needed for the structural usage.
Tensional Ability of Concrete with Recycled Coarse Aggregate
In a research conducted by Benjamin (1997) he concluded that “the strength of the recycled materials is of paramount importance in the design of concrete roads, railways etc” (p.28). Concrete constituents are also required to withstand tensile stresses that come from restraint to contraction due to the loss of moisture or temperature changes.
Avaan(2007,p.2). Stated that
“Unlike metals it is not easy to take record of the strength of concrete, in direct tension and indirect techniques, which have been established for evaluating this property.The concrete strength in direct tension is determined by split cylinder test. The magnitude of the imposed tensile stress at failure is expressed as:
Fct = 2F/(pi*Ld) —— (2.1)
Where; F = Applied load
L = Length of cylinder
d = Diameter of cylinder”(p.59).
Flexural Ability of Concrete Obtained From Recycled Coarse Aggregate
According to Moses(2001,p.4) the flexural ability of concrete has been known to be the modulus of breakdown that is used to evaluate tensile strength as determined from tests on beams. The standard approved size of beams for flexural examination according to (BS 1881) is 150mm x 150mm x 700mm. Moreover, the society of America for testing materials (A. S. T. M) as recorded by Gomez-Sseberon(2002),states that “the dimension of the beam should be at least 50mm longer than three times its depth and its width should be not exceed one and half times its depth. The minimum depth of width should be at least three times the highest size of aggregate and should not be less not less than 50mm. This is obtained from simply aided beam loaded at the third points. The outcome of the bending moment induces cognitive and tensile stresses in the top and bottom of the beam respectively”(p.76). Based on Avaan (2007) evaluation,
“the beams flexural strength is given as:
fct = FL/(b*d*d) ——- (2.2)
Where; F = Applied load
L = Effective span
b, d, = Breadth and depth of beam respectively.
The capability in bending can be defined or referred to as the maximum stress on the tensile side of a point at the instance of failure. The ultimate capability of under reinforced or re-enhanched beams in flexure is insensitive to the model used to represent the stress-strain similarities”(p.10).
It is only where failure occurs as a result of crushing of concrete in compression that the various stress-strain relationships may lead to various evaluated maxima ability (Yang, et al, 2008).
Conditions Influencing The Capabilities of Concrete With Coarse Recycled Aggregate
The capability of concrete is influenced by a number of conditions such as;
Water-Cement Ratio: certain properties of the concrete are influenced by the quantity or the amount available in the cement paste. This lead to an important procedure or technique of obtaining some basic and vital properties one of which is the workability and another been the ability of concrete. The required quantity of water needed in other to obtain quality outcomes is based on the peak size, and in some instances the shape of the aggregate(Sanchez de Juan,et al,2004).
The quantity of cement needed for a specific concrete strength changes or varies significantly for various aggregates. This is dependent on the strength and modulus of squeezing the aggregate specifically under considerations and also on the free water content needed for complete performance of Aggregate.Following a prolonged and detailed examination and some experiments by various researchers in this related field under research a conclusion was arrived at that the particle sampling of the aggregate basically influences the amount of a mixture of water needed for proper performance. It has been revealed from past experiences that the increment in the ratio of smooth materials advances the water needed and this results to a minimal concrete ability unless the cement components is stepped up. It should be taken into consideration that the usage of recycled sand was excluded, as a result of this, its intake ability, which would no doubt manufacture a shrinkage influence.
3. Extensive Supplement: Through the addition of extensive supplement entails increase by 10% in any condition of aggregate class. This can be explained by that the axial force, which is obtained by extension of concrete, makes bigger shear areas and slimly cracking width. It was observed after examining some results obtained then researchers discovered that the wider compressive ability zone enhances the compressive persistence and the slimly cracking width positively changes the interlocking workability. Benjamin (1997) “revealed the influence of water-cement proportion and aggregate class on shear capability of recycled concrete [RC] beams excluding shear reinforcement which is gotten by V/(bd), where V denotes shear force at diagonal cracking, compared with shear strength of virgin concrete [VC], the compression strength of (RC) shows 20% reduction at most”(p20).
The holding ability is one of the most vital characteristics that shows the difference among recycled aggregate from natural aggregates, and it can have an effect both on fresh and strong concrete properties. It have been discovered that the absorption capacity of the aggregate which has been recycled was affected extensively by other additives which are gotten from related samples which is known to be of greater importance and these must be made aware prior to it been put in use by the required areas of application in order to obtained relevant result for the production of concrete so that the characteristics can be in a such a way that it can be under a monitored routine(Abraham,1998). Sand which have undergone recycling should not be included in the process due to the fact that it has something to do with its capacity absorption which will consequently lead to an output which is not favorable. The performance and workability of the output which have been recycled following the recommended procedures and quality result yielding technique is affected by its holding ability. The influence on the application of the crushing technique applied for the production of concrete that are new, constitutes the factors that brings about alot of variation in its capability.
The amount of additives or supplement affects the techniques employed. The methodologies employed in the period or span of manufacturing has a lot of conditions influencing properties that made up the concrete, in view of compacting the undesirable outcome ,some safety or perceptional measures must be taken in order to avoid these unfortunates results emanating so that maximum quality can be achieved when homogenous quantity is been ensured so as to minimized predictive appearance during the process. The rate at which water is been giving out to the atmosphere determines the proportion by which constituents are been brought together that are still surviving because of its water holding and as a result embeds itself into air forming supplementary defects on concrete’s ability but in the absence of these it will be difficult to achieve the desired output. Components that are flexible can have defects not only in their bending moment but also from shearing advancement. Various researchers like Yang et al,(2005) In this related field,researchers all over the world revealed that beams fail as a result of persistence along its axis,this research further and discovered that the pattern of failure characteristics of recycled concrete beams were same to usual concrete beams.
Classes of Re-enhanced Failure are as follows:
- Flexible failure. It is the first form of failure that is visible at peak moments.
- Diagonal failure.
Effect of Crushing Method Applied
Moses(2001) in work stated that ”the crushing procedure (mechanical or manual) of concrete produces coarse aggregate for the manufacturing of recent concrete is one of the conditions that influences the ability of the concrete. The crushing method and the dimension of the recycled aggregate also was studied and proven to have an effect on the quantity of adhered mortar” (p.67).
Effect of procedures of Preparation
During the duration of mixing concrete constituents, safety must be taken to make sure that a reoccurring and equal mass is achieved to prevent low quality concrete as a result of this limitation which would on the long-run or in a short-run have on the constituents of the concrete, adequate safety should be taken during the period of laying and compaction to reduce the probability of appearance of bleeding, segregation and honey comb.
The Effect of Curing
Avaan(2008) in his work on concrete beams discovered that “the quality of concrete is obtained by the way in which curing is accomplished”(p.26). The escape of water from the cast beam or concrete is an indication that the constituent grains of the recycled aggregate will be held together with lesser force, and as a result exposes the different possibility strategies for air particles to occupy the space giving rise to voids in the final concrete.
Flexural Tension Failure of Concrete with Recycled Materials
Flexible failure normally results when the various position are observed. The first class of crack is usually referred to as a web-compression crack, the second class being noted as a flexural-compression crack. It is proven that the value of diagonal tension is basically not determined. The diagonal crack commences from the minimum flexural crack and further advancement under the compression loading.
Diagonal Shear Tension And Failure of Concrete Beam With Recycled Aggregate
Moses(2001) revealed that ” beams, where compression influence is vital, diagonal cracks are formed as of result of diagonal tension emanating from a combination of compression and flexural tension”(p.20). It is proven that the value of diagonal tension is basically not determined. For this particular location or point, it is very normal for beams or concrete which posses compression reinforcement to put together the figure of shearing unit stresses, usually that of the one in the vertical direction (Zan-zan, 1996). It is important to note that most of the failures that are tagged compression failures are not actual compression failures but they are diagonal tension failures.The diagonal crack commences from the minimum flexural crack and further advancement under the compression loading(Moses,2001).
A diagonal tension failure can be stated as a step up crack in the shear range prolonging from tensile reinforcement in direction that is almost concentrated in load sectioning the level of tensile reinforcement at an angle of approximately 450. This results when the compression force is relatively larger and bending moment rather minimum. It normally occurs when the load is near to the aid. Large diagonal cracks emanates from the support to the load(Sanchez de Juan,2004). The form in which diagonal failures occur and continually develop is influenced by some factors amongst which is flexural stress.
Yang, et el(2oo8 ). Experimental data reveals that in ideal strength concrete, the compression crack emanates in the strong cement matrix, and around the relatively harder coarse aggregate. In advanced strength concrete where the matrix is relatively harder, the shear crack goes through the matrix as well as the aggregate, resulting in a fine crack platform. Abraham, ( 2007 ). carried a research work on the failure patterns of recycled concrete beam and discovered that the failure of the concrete obtains from its weakest zones. The weakest zone being in these moderate strength concretes, the recycled aggregates themselves. In moderate strength conventional concretes, the platform is the weakest area, furthermore, this is not the situation when the concrete is composed of recycled aggregates, as what results in high strength concretes where the failure is in the direction of the aggregates. Abraham(1998 ) His research work also showed that “the splitting tensile failure of concrete composed of a high quantity of recycled aggregates”(p.18).
Results Obtained in 7 and 28 Days
Latest concrete which is usually obtained from recycled concrete aggregate has in general terms the same properties(Moses,2001,p.9).
Glass Concrete Aggregate
Avaan(2007,p.1) reviewed that “Field analysis has revealed that crushed and screened waste glass may be used as a sand substitute in concrete. All glass materials that have been disposed or discarded as not been useful can be utilized in the construction of beams and all other forms of concrete works. This includes even those that have been rejected for the purpose of recycling them to be used in the bottling of products. Most of the glass that is utilized in concrete application are those that have been rejected for recycling for other uses usually fluorescent bulbs and others which contain some form of contaminants.
Abraham(1998 ) Showed that “research has been carried out on types of glass and other supplements to prohibit or decrease the alkali silica reaction and thereby maintain finished concrete strength”(p.98). Some form of studies is still greatly needed for a decision to be taken to utilize glass culets in concrete analysis. The use of any form materials at all for the purpose of constructing beams or other uses help in the preservation of our landfills. Recycling of materials for use in various ways will help in curtailing the environmental problems that result from the excavation of the materials and again preserve the materials for longer use in the future.
Latest concrete which is usually obtained from recycled concrete aggregate has in general terms the same properties(Yang et al,2008,p.7).
The holding capacity of the recycled aggregates and the nature of the aggregates can influence the workability of the listed concretes. It is dependent on which type of crusher is employed. The aggregate components of recycled concrete compare well to alternative aggregates in that they contain fine particle shapes, high moisture holding capacity, and minimal specific gravity. It is thus advisable that the type and nature of any recyclable material that will be adopted should depend on the use to which the beam is to be put and most importantly the materials that are available.
It will be important to note that making use of recycled concrete materials inmaking concrete beams will eventually lead to decrease in the performance of such beams or the any concrete product that is obtained from it. This can be accounted for as a resukt of the high ability of this recycled particles to take in water. This form of result is obtainable when materials with veryu light weight are used in the construction of concrete structures. But from studies that have been carried out over time it was noticed that the strength or duability of the lightwiegt materials was close that of the concretes made with conventional materials.This is because the paste quality of the light weight materials can be enhanced considerably.
The following deduction have been made from previous studies that have been carried out
- The complete exchange of conventional materials with recycled materials results in a reduction in the strength of the concrete up to 15%. A replacement that is close to say 49%, in the mix with 340kg/m3, will result to a reduction in the strength of the concrete material to about 4%.
- The utilization of recycled materials to make concrete give rise to final products with less performance as compared to those of conventional materials This is basically as the result of the high number of the pore spaces within the final product. Nevertheless researchers are still not so certain as regards the amount of water that is taken by the concrete or other products made from recycled materials or aggregate.
- The interface quality of beams or other products made from recycled materials is less than that made from light weight materials.This is believed to be as a result of the lesser ability of the recycled materials to absorb water and as such decrease their ability to make bonds properly.
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Avaan,J. (2007). Mechanical properties of concrete with recycled coarse aggregate. Abuja: Oracle Books.
Benjamin,F. (1997). Material behavior of recycled concrete aggregate. Makurdi:Santos Press.
Gomez-Soberon,J. (2002) Shrinkage of concrete with replacement of aggregate with recycled concrete aggregate. ACI Spec. Publ. 475-496.
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Yang, K.H., Chung, H.S., Ashour, A. (2008) Influence of type and replacement level of recycled aggregates on concrete properties. ACI Material Journal, V. 105, br. 3, May-June, str. 289-296.
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