Crushed Concrete Research Articles

Strengthening of structurally damaged wide shallow RC beams using externally bonded CFRP plates

Reinforced concrete wide shallow beams (WSBs) are commonly used in the joist flooring systems. The structural behavior of WSBs strengthened with carbon fiber reinforced polymer (CFRP) reinforcement was studied on isolated beams and as part of full-scale building. The effect of structural damage on the performance of WSBs flexurally strengthened with CFRP plates was investigated and presented in this paper. Eight full-scale WSBs were tested under four-point bending up to failure. Seven beams were strengthened with CFRP plates bonded to the soffit of the beams and one beam was unstrengthened serving as control. Prior to strengthening, the beams were subjected to different levels of damaging by preloading to 30-95% of the beams' flexural capacity. One beam was fully damaged by preloading to failure and repaired before strengthening by replacing the crushed concrete. The data showed that the pre-damaged strengthened beams exhibited ultimate capacities up to 8% lower than those of the undamaged strengthened beams. However, the load carrying capacities of pre-damaged strengthened beams were more than those predicted by ACI 440 design guide, fib Bulletin 14, and JSCE design recommendations. Both fib Bulletin 14 and JSCE design recommendations gave very conservative predictions with average ratios of experimental to predicted ultimate capacity of 2.02 and 2.35, respectively. More accurate predictions were obtained by ACI 440 design guide as the corresponding ratio was 1.24. These results indicate that strong confidence and reliability can be placed in applying CFRP strengthening to structurally damaged WSBs.

Manipulating soil microbial communities in extensive green roof substrates

There has been very little investigation into the soil microbial community on green roofs, yet this below ground habitat is vital for ecosystem functioning. Green roofs are often harsh environments that would greatly benefit from having a healthy microbial system, allowing efficient nutrient cycling and a degree of drought tolerance in dry summer months. To test if green roof microbial communities could be manipulated, we added mycorrhizal fungi and a microbial mixture (‘compost tea’) to green roof rootzones, composed mainly of crushed brick or crushed concrete. The study revealed that growing media type and depth play a vital role in the microbial ecology of green roofs. There are complex relationships between depth and type of substrate and the biomass of different microbial groups, with no clear pattern being observed. Following the addition of inoculants, bacterial groups tended to increase in biomass in shallower substrates, whereas fungal biomass change was dependent on depth and type of substrate. Increased fungal biomass was found in shallow plots containing more crushed concrete and deeper plots containing more crushed brick where compost tea (a live mixture of beneficial bacteria) was added, perhaps due to the presence of helper bacteria for arbuscular mycorrhizal fungi (AMF). Often there was not an additive affect of the microbial inoculations but instead an antagonistic interaction between the added AM fungi and the compost tea. This suggests that some species of microbes may not be compatible with others, as competition for limited resources occurs within the various substrates. The overall results suggest that microbial inoculations of green roof habitats are sustainable. They need only be done once for increased biomass to be found in subsequent years, indicating that this is a novel and viable method of enhancing roof community composition.

EFFECT OF USING STEEL SLAG AGGREGATE ON MECHANICAL PROPERTIES OF CONCRETE

This study presents an evaluation of the physical and mechanical properties and characteristics of steel slag aggregate concrete in comparison with the typical crushed limestone stone aggregate concrete. Hardened concrete consist of more than 70% aggregate due to the high demand in building construction and the increase of the amount of disposed waste material, suppliers and researchers are exploring the use of alternative materials which could preserve natural sources and save the environment. In this study, steel slag was used as an aggregate replacement in conventional concrete mixes. Steel slag which is mainly consists of calcium carbonate is produced as a by-product during the oxidation process in steel industry. Steel slag was selected due to its characteristics, which are almost similar to conventional aggregates and the fact that it is easily obtainable as a by-product of the steel industry. As a result, utilization of steel slag will save natural resources and clean environment. Furthermore, results have shown that slag aggregate has better abrasion factor and impact value than conventional aggregate. Thorough investigation of the results have indicated that the amount of increase in compressive strength at age of 7 days are much more than that of age 28 days for all types of aggregate replacement. This indicates that the added slag could work as accelerator at early age while at 28 days age, the effect is reduced. The fine slag replacement scores the highest effect.

Mechanical recycling of EOL concrete into high-grade aggregates

Recycling End of Life (EOL) concrete into high-grade aggregate for new concrete is a challenging prospect for the building sector because of the competing constraints of low recycling process cost and high aggregate product quality. A further complicating factor is that, from the perspective of the environment, there is a strong societal drive to reduce bulk transport of building materials in urban environments, and to apply more in situ recycling technologies for Construction & Demolition Waste. The European C2CA project investigates a combination of smart demolition, grinding of the crushed concrete in an autogenous mill to increase the liberation of cement mortar from the surface of aggregates and a novel dry classification technology called ADR to remove the fines. The feasibility of this recycling process was examined in a demonstration project involving 20,000tons of EOL concrete from two office towers in Groningen, the Netherlands. Results show that the +4mm recycled aggregate compares favorably with natural aggregate in terms of workability and the compressive strength of the new concrete, showing 30% higher strength after 7 days.

Mix proportioning and performance of a crushed limestone sand-concrete

Satisfying the ever-growing demand of concrete aggregates poses a problem in many parts of the world due to shortage of natural sand. Moreover, to conserve natural resources and protect civil engineering infrastructures, there is a need to find alternative materials. Crushed stone sand has been identified as a potential substitute material for natural sand in making good quality concrete. The main objective of the present investigation is to determine an adequate mix design method and evaluate engineering properties of crushed limestone sand concrete mixtures in both the fresh and hardened sates. More than thirty concrete mixtures were examined. The results indicate that water demand and cement paste content in crushed sand concrete are generally higher than that used in similar conventional concrete. Good mechanical properties were obtained for concrete using crushed limestone sand as fine aggregates with a superplasticizer. However, a higher than normally used dosage of superplasticizer is required in these concrete mixtures and the optimum dosage of the superplasticizer needs to be determined for each cement and sand content.

Mix proportioning and performance of a crushed limestone sand-concrete

Satisfying the ever-growing demand of concrete aggregates poses a problem in many parts of the world due to shortage of natural sand. Moreover, to conserve natural resources and protect civil engineering infrastructures, there is a need to find alternative materials. Crushed stone sand has been identified as a potential substitute material for natural sand in making good quality concrete. The main objective of the present investigation is to determine an adequate mix design method and evaluate engineering properties of crushed limestone sand concrete mixtures in both the fresh and hardened sates. More than thirty concrete mixtures were examined. The results indicate that water demand and cement paste content in crushed sand concrete are generally higher than that used in similar conventional concrete. Good mechanical properties were obtained for concrete using crushed limestone sand as fine aggregates with a superplasticizer. However, a higher than normally used dosage of superplasticizer is required in these concrete mixtures and the optimum dosage of the superplasticizer needs to be determined for each cement and sand content.

Characterization of Crushed Brick Lightweight Concrete Reinforced with Palm Fibers

This study was aimed to investigate the effect of palm fibers on the properties of lightweight concrete.Such lightweight concrete was produced from coarse lightweight crushed brick and fine lightweight crushe d brick (CLWA and FLWA). Different percentages of palm fiber; 0, 0.25, 0.5 0.75, 1, and 1.25% based on volumetric fractions were included with lightweight concrete mixes. The properties tested include fresh density, compressive strength, splitting tensile strength, static modulus of elasticity, absorption,flexural strength, and toughness indices. The results show that the use of 0.75% of palm fiber would raise the compressive strength, splitting tensile strength and flexural strength of the lightweight con crete by about 11%,47% and 18%, respectively. The same percentage of palm fibers would significantly enhance the toughness performance of crushed brick lightweight concrete.

Recycled construction and demolition concrete waste as aggregate for structural concrete

In major Egyptian cities there is a surge in construction and demolition waste (CDW) quantities causing an adverse effect on the environment. The use of such waste as recycled aggregate in concrete can be useful for both environmental and economical aspects in the construction industry. This study discusses the possibility to replace natural coarse aggregate (NA) with recycled concrete aggregate (RCA) in structural concrete. An investigation into the properties of RCA is made using crushing and grading of concrete rubble collected from different demolition sites and landfill locations around Cairo. Aggregates used in the study were: natural sand, dolomite and crushed concretes obtained from different sources. A total of 50 concrete mixes forming eight groups were cast. Groups were designed to study the effect of recycled coarse aggregates quality/content, cement dosage, use of superplasticizer and silica fume. Tests were carried out for: compressive strength, splitting strength and elastic modulus. The results showed that the concrete rubble could be transformed into useful recycled aggregate and used in concrete production with properties suitable for most structural concrete applications in Egypt. A significant reduction in the properties of recycled aggregate concrete (RAC) made of 100% RCA was seen when compared to natural aggregate concrete (NAC), while the properties of RAC made of a blend of 75% NA and 25% RCA showed no significant change in concrete properties.

Long-Term Deflections of Crushed Limestone Sand Concrete Beams

Creep tests of three crushed limestone sand concrete beams were conducted. The mid-span creep deflections and creep deflection coefficients of the beams in the first six months were measured. The results show that the creep deflection is significantly affected by the environmental humidity and temperature conditions. The formula of the mid-span creep deflection is derived based on the creep coefficients for simple supported beams. The mid-span creep deflections of beams are calculated using the CEB-FIP 90, ACI 209, and B3 models to predict the creep coefficient separately. Comparisons between the calculated values and experimental results indicate that the coefficients obtained using the ACI 209 model fit the results best. The formula of the creep coefficient is derived from the mid-span creep deflection. The creep coefficient of crushed limestone sand concrete is calculated from the measured mid-span creep deflection, and a best-fit formula is proposed for the creep coefficient.

Hydrodynamic characteristics of a new permeable pavement material produced from recycled concrete and organic matter

The aim of the present study was to evaluate the hydrodynamic characteristics of a new material to be used for permeable and purifying pavements in urban areas. The new material is a mixture of crushed concrete, to provide structural support, and a compost mix intended to retain and biologically treat stormwater pollutants. The first part of this study was to evaluate the hydraulic conductivity of the material at different mixing ratios to define the range of materials suitable for urban drainage applications. The second part of the study involved using tracing experiments to quantify the effects of the pollutant transport mechanisms occurring during the water infiltration process. These experiments were conducted under steady state flows condition using a conservative tracer (NaCl). The results demonstrate that while the addition of compost significantly reduced the permeability of the concrete mix, it was still suitable for use as a paving material in an urban environment. The increased residence time of the stormwater pollutants due to the addition of the compost mix was shown to have a positive effect on the biological treatment of the stormwater pollution.

Modeling phosphorus removal in wet ponds with filter zones containing sand or crushed concrete

Generally, wet ponds are constructed only to reduce the hydraulic load of downstream receiving water bodies. Often most particulate matter will be retained, whereas dissolved nutrients mostly will be unaffected by the pond due to short retention times. A suite of lab-experiments have demonstrated that crushed concrete has high affinity for dissolved phosphorus (TDP), and potentially could be an effective new measure to reduce discharge of phosphorus (P) to downstream located P-limited lakes and estuaries. To verify this potential we have developed a dynamic model for a combined sedimentation and infiltration pond in Denmark, using the software PowerSim. The model simulates retention of P and suspended particulate matter (SPM). It is possible to change the description of filter material in the model to either a traditional sand filter or a filter of crushed concrete, and thereby demonstrate the P-retention efficiency of the different materials. Two scenarios with changing wet volume and storage volume of the pond indicated that 400 and 50m3pr. reduced hectare (red. ha), respectively, would be optimal for retention of particles. In combination with this result, the model showed a significant increase in TDP retention with a concrete filter (≈60%) compared to a traditional sand filter (≈10%). This only applies for water actually percolating through the filters and not for the overflow. Because concrete is an alkaline material, pH in the discharge to the receiving water body will be high (>9.5) for approximately 100 days and then decrease to neutral. If adequate precautions against high pH in the discharge are put in place, crushed concrete can reduce the discharge of TDP to sensitive receiving water bodies.

Properties of porous concrete from waste crushed concrete (recycled aggregate)

The purpose of this study was to develop porous concrete with acceptable permeability and strength using recycled aggregate from waste crushed concrete. The optimum mix proportions were employed to prepare porous concretes using normal and recycled aggregates. Tests carried out on porous concrete were: void ratio, coefficient of permeability, compressive and flexural strengths. The effect of recycled aggregate on total void ratio, strength and permeability was examined. Styrene butadiene rubber-based redispersible polymer powder and latex were introduced to mixtures to improve strength properties. The total void ratio of porous concrete incorporating recycled aggregate was larger than that of porous concrete with normal aggregate. The addition of polymer modification resulted in a slight decrease in total void ratio regardless of type of aggregate. The compressive strength of porous concrete using recycled aggregate was lower the one using normal aggregate. However, the compressive strengths of porous concretes using normal and recycled aggregates were significantly improved by 57% and 79% respectively, due to polymer modification. The use of recycled aggregate along with optimum content of polymer could produce acceptable porous concrete with both enough drainage and strength properties.

Study on mechanical properties of steel fiber reinforced autoclaved lightweight shell-aggregate concrete

The mechanical properties of autoclaved propylene oxide sludge shell-aggregate (POSS-A) concrete are studied in this paper. Under the condition of a fixed water cement ratio, a series of experiments were carried out to investigate the effect of steel fibers content of autoclaved POSS-A concrete on the mechanical properties. The results are compared with those of sintering concrete and crushed stone concrete. The experimental results indicate that adding steel fiber in autoclaved POSS-A concrete can slightly enhance the cubic compressive strength but remarkably improve flexural strength. Because of special spherical structure and appearance of POSS-A, the reinforced effect of steel fiber on autoclaved POSS-A concrete is superior to those of steel fiber on other two types of concretes. Flexural strength of steel fiber reinforced autoclaved POSS-A concrete improve 108% when volume fraction of steel fiber increase from 0% to 2.0%, which is higher than 92% of sintering aggregate concrete and 78% of common concrete.

Large-Scale Direct Shear Testing of Recycled Construction and Demolition Materials

Abstract Laboratory large-scale direct shear tests were carried out on five different recycled construction and demolition materials, such as crushed concrete (CC), crushed rock (CR), crushed brick (CB), reclaimed asphalt pavement (RAP), and recycled glass (RG). The shear strength parameters were evaluated with a large shear test machine for different values of normal stress ranging from 30 to 200 kPa. Resulting values of cohesion were found to vary in a wide range between 8.55 kPa to 284.5 kPa, whereas coefficient of internal friction varies between 44.6° to 52.1°. The failure envelopes for all materials investigated are straight-line failure envelopes. Crushed rock and crushed concrete showed high cohesion of 284 kPa and 154 kPa, respectively, whereas reclaimed asphalt pavement and recycled glass showed low cohesion of 8.55 kPa and 14 kPa, respectively. Meanwhile, crushed brick showed a medium cohesion of 61.2 kPa. Further, the volumetric behaviours of the recycled materials are dilatancy except for reclaimed asphalt pavement at low normal stress. The results of the shear strength tests indicate that CR, CC, and CB and blends of RAP and medium recycled glass (MRG) with other materials can be viable materials to be sustainably used in pavement sub-base applications.

Reclaimed Asphalt Pavement Stabilized Using Crushed Concrete Waste as Highway Pavement Material

Pavement rehabilitation and reconstruction generate a large volume of reclaimed asphalt pavement (RAP) waste. Also, large quantities of crushed concrete waste (CCW) are generated from building demolitions and constitute a principal component of municipal solid waste consisting of concrete, sand, brick, rock, metals, and timber. This paper present the results of a laboratory evaluation of the characteristics of RAPs stabilized using CCW with a view toward determining their suitability for use as flexible pavement material. The mixtures were subjected to British Standard light (standard Proctor) compactive efforts to determine the compaction characteristics and California bearing ratio (CBR). Test results show that the properties of RAP waste improved with CCW treatment. The maximum dry density decreased, and the optimum moisture content increased, with increased CCW content in the mixes. Optimum CBR values of 28.06 % (unsoaked) and 32.81 % (soaked for 24 h) were recorded for a 50 % RAP + 50 % CCW mix. With the potential of a time-dependent increase in strength in view, the 50 % RAP + 50 % CCW mix with a recorded CBR value of 32.81 % (soaked for 24 h), which satisfied durability requirements with insignificant water absorption, can be used as a sub-base material in flexible pavement construction. This research provides results of the evaluation of RAP waste stabilized using CCW as a highway construction material, as based on CBR determination. Further work may be encouraged in order to assess the resilient modulus of this material under cyclic load.

Crushed Concrete as a Phosphate Binding Material: A Potential New Management Tool

To avoid eutrophication of receiving waters, effective methods to remove P in urban and agricultural runoff are needed. Crushed concrete may be an effective filter material to remove dissolved and particulate P. Five types of crushed concrete were tested in the laboratory to evaluate the retention capacity of dissolved P. All types removed P very effectively (5.1-19.6 g P kg(-1) concrete), while the possible release of bound P varied between 0.4 and 4.6%. The retention rate was positively related to a decreasing concrete grain size due to an increasing surface area for binding. The P retention was also related to a marked increase in pH (up to pH 12), and the highest retention was observed when pH was high. Under these circumstances, column experiments showed outlet P concentrations <0.0075 mg P L(-1). Furthermore, experiments revealed that release of heavy metals is of no importance for the treated water. We demonstrate that crushed concrete can be an effective tool to remove P in urban and agricultural runoff as filter material in sedimentation/infiltration ponds provided that pH in the treated water is neutralized or the water is diluted before outlet to avoid undesired effects caused by the high pH.

Feasibility Study on Building-Derived Concrete Debris for Use in Highway Construction

Abstract The current American Association of State Highway and Transportation Officials standard on crushed concrete in base applications (M 319-02) allows up to 5 % brick by mass, and more with the approval of the engineer; however, in some regions the brick content may be greater than 10 %. More than 41 states allow the use of crushed concrete in highway applications, but only a handful allow the use of building derived concrete (BDC) or mixed stream crushed concrete. Barriers to increasing the appropriate use of BDC in highway applications include a lack of data comparing BDC properties and performance to natural aggregates, as well as data that pavement engineers can use for design. This research has focused on characterizing BDC that was screened to meet New Hampshire Department of Transportation specifications. The gradation, optimum water content, unit weight, and resilient modulus were measured for the BDC and for the control materials, which were a crushed stone and a sand. The resilient modulus was measured using both a laboratory triaxial cell, and a light falling weight deflectometer (LWD) in a test pit. The resilient modulus of the BDC exceeded that of the control materials as measured in the laboratory and using the LWD. In addition, the laboratory resilient modulus showed good correlation with the LWD stiffness. These results suggest that BDC would perform as well as natural aggregates in base course applications.

Concrete Made with Coarse Concrete Aggregate: Influence of Curing on Durability

This article will present the results of experiments conducted to determine the influence of different curing conditions on the durability of recycled aggregate concrete (RAC) made with coarse crushed concrete. Four different curing conditions that represent a wide range of quality control production were tested. The curing conditions tested ranged from uncontrolled outer environment conditions to standard defined temperature humidity curing conditions. The properties analyzed were shrinkage, water absorption by immersion and capillarity, carbonation, and chloride penetration. The article concludes that RAC is affected by curing conditions in much the same way as conventional concrete.

Comparison of Specifications for Recycled Concrete Aggregate for Pavement Construction

Abstract This paper reviews existing specifications, specifically for the application of crushed concrete or recycled concrete aggregate (RCA) as pavement material for unbound subbases and basecourses. While the use of recycled crushed concrete is not new internationally, its application in Australia is unique as it is being commonly used as a granular basecourse/subbase supporting thin bituminous seals (asphalt or spray seal/chip seal). Commonality of specifications is explored and differences that exist are questioned. In light of practice outside of Australia, limitations by Australian authorities placed on recycled material inclusions other than crushed concrete are raised. In this paper, two South Australian-based RCA products, which were designed for use as pavement bases, are compared with current engineering specifications. The RCA products performed well in terms of resilient modulus and permanent deformation. However, properties such as abrasion resistance and wet/dry strength may restrict the application of the material if current specifications are justifiable.

PROPERTIES OF HARDENED CONCRETE USING CRUSHED CLAY BRICK AS AGGREGATES

This paper provides the result of an investigation to use of crushed clay brick asaggregates in producing concrete. Eight different crushed clay brick aggregate concretes wereused in this investigation. Compressive strength, splitting tensile strength and pulse velocity ofcrushed clay brick aggregates concrete were determined and compare to natural aggregateconcrete. The compressive strength of crushed clay brick aggregates concretes were alwayslower than the compressive strength of natural aggregates concrete regardless the age ofconcrete, but the crushed clay brick aggregates concrete showed better performance as the age ofconcrete increases and average reduction in compressive strength were 33.5% at the age of 7days but it becomes only 20% at the age of 56 days compared to natural aggregates concrete. Thesplitting tensile strength of crushed clay brick aggregates concrete were always lower thannatural aggregate concrete, the reduction in splitting tensile strength of crushed clay brickaggregates concrete is ranging between 11 and 26% with an average reduction of about 18.5%compared to natural aggregates concrete. The pulse velocity of crushed clay brick aggregatesconcrete were also lower than natural aggregates concrete, the reduction in pulse velocity ofcrashed clay brick aggregates concrete is ranging between 6 and 22% with an average reductionof about 14% compared to natural aggregates concrete.