Compaction Energy Research Articles

Effects of Mixture and Aggregate Type on Over-Compaction in Hot Mix Asphalt in Tennessee

Correct compaction is vital for asphalt mixture service life. An adequately compacted mixture with inferior properties can achieve better performance than a mixture with excellent properties but poorly compacted. This study investigated resistance to damage caused by over-compaction by utilizing the locking point concept. Over-compaction might cause damage to the aggregate structure and decrease service life. The locking point is defined as the moment during mixture compaction at which an aggregate skeleton is developed and becomes stable. Beyond the locking point, more compaction energy does not significantly increase mixture density and can damage aggregate particles. A total of 15 mixtures was utilized and evaluated using the gyratory compactor. Among them, five dense-graded plant mixtures contained different aggregates and binders, and 10 laboratory mixtures (three types: the surface, the base, and stone mastic asphalt [SMA]) were designed with the most popular coarse aggregates in Tennessee: hard limestone, soft limestone, gravel, and granite. The results of this study show that the highest locking point was reached by the mixtures containing gravel. The SMA mixtures have, on average, lower locking points than the dense-graded mixtures. Most of the dense-graded mixtures made with crushed stones failed in the range of +20 to +30 gyrations, whereas the samples made with gravels failed in the range of +30 to +40 gyrations, indicating that gravel seems to be the most resistant to damage.

Earth construction: Field variabilities and laboratory reproducibility

Building construction is a major polluting sector. As a result, there is increasing global interest in the development of sustainable building materials with low environmental impact. Earth-based materials are among the materials of interest and building with earth-based materials has thus received a particular renewal of attention. Previous research has focused on the physical characteristics and durability of these materials. The aim of this study is to assess the variability of materials made in-situ and their reproducibility in the laboratory using an automatic normal Proctor machine with different compaction energies. Both cob and light earth were investigated. Cylindrical and prismatic specimens were produced on-site and in the laboratory: cob was made of silt, silty clay, sandy silt, and flax straw; and a separate layer of light earth was made of elastic silt and reed fibres. An experimental program was designed to evaluate the properties of the materials in terms of their water content, density, porosity, compressive strength, and thermal conductivity. The results revealed that the in-situ densities could be reproduced in the laboratory with compaction energies of 0.6 MJ/m3 and 0.2 MJ/m3 for cob and light earth, respectively. These compaction energies will allow the research to produce laboratory specimens that were representative of the materials implemented on-site. Regarding the compressive strength, the values obtained in the laboratory were higher than those of the in-situ specimens. Correction factors of 0.88 and 0.67 for cob and light earth. These values should be applied to calibrate the laboratory results in relation to in-situ. Concerning the thermal conductivity, the values obtained in the laboratory were similar for cob and higher for light earth. A correction factor of 0.87 should be applied to calibrate the laboratory results to those obtained in-situ.

Evaluation of the influence of compaction energy on the resilient behavior of lateritic soil in the field and laboratory

This article presents the study of the resilient behavior of three soil horizons from a deposit of lateritic soil employed in a pavement structure in Rio Grande do Sul, Brazil. The use of lateritic soils in pavement layers is a common practice in Brazil and due to its peculiarities, its behavior must be investigated. The methodology consisted of physical and chemical characterization and resilient modulus determination. Samples from the three horizons, compacted at standard, intermediate and modified energy, were analyzed. In addition, undisturbed samples extracted from the interior and top layer of the embankment were submitted to repeated load triaxial tests for resilient modulus determination. The results indicated that the soil exhibit good behavior for pavement subgrade applications, perhaps as subbase or base course layers. The compound and universal models yielded the best correlation coefficients. Furthermore, the results showed that as the compaction energy increased, the resilient modulus also increased, as long as they are within the optimum water content and compaction degree limit. However, when subjected to immersion in water for four days, the resilient behavior decreased about 73% in relation to unsaturated samples.

Resilient Response of Cement-Treated Coarse Post-Glacial Soil to Cyclic Load.

Stabilisation with cement is an effective way to increase the stiffness of base and subbase layers and to improve the rutting of subgrade. The aim of the study is to investigate the effect of different percentages of cement additives (1.5%, 3.0%, 4.5% and 6.0%) on the resilient modulus of coarse-grained soil used on road foundations. The influence of the compaction method, the standard Proctor and the modified Proctor, as well as the sample curing time is analysed. The cement addition significantly increases the resilient modulus and reduces the resilient axial strain. Extending the curing time from 7 to 28 days also improves the resilient modulus. The change in the compaction energy from standard to modified does not increase the resilient modulus of the stabilised gravelly sand due to its compaction characteristics. The test results of the resilient modulus of the gravelly sand stabilised with cement indicate the possibility of using it as a material for the road base and subbase due to meeting the AASHTO requirements. However, the non-stabilised gravelly sand does not meet the above requirements. It has been sheared during cyclic tests at the first load sequence, regardless of the compaction method.

The Use of PT Petro Kimia’s by-Product Gypsum as Fill Materials

Gypsum is a by-product of the Phosphoric Acid factory PT Gresik Petrochemicals; it is produced around 1,200,000 tons/year. In order to reduce the amount, an effort needed to use gypsum as fill materials. For this purpose, the problem needs to be considered is that gypsum should not contain substances that harmful to the environment and meet the fill materials requirements. In order to answer all these questions, chemical tests were carried out to determine its heavy metal content. Gypsum plasticity and its particle size distribution were determined by conducting Atterberg limit and sieve analysis tests. Compaction test and CBR test were also carried out to determine the density and its strength. Those results were then analyzed using "The Fifteen Point Method" to obtain a relationship curve between dry density (d) and soaked-CBR. This curve was important to determine the soaked-CBR that can be achieved by gypsum materials in the field with different compaction energy 90%, 95%, and 100% of maximum compaction energy. Chemical test result shows that all heavy metals content in gypsum material are far below the regulatory limit; therefore, it is safe for the environment. Besides, Gypsum is non-plastic (NP) material and it is classified as A-4 (AASHTO) or SM (USCS); it means that Gypsum is very good for fill materials and safe to the environment. In addition, the result from the Fifteen Point Method shows that the minimum soaked CBR value is 13% achieved by using 90% of maximum compaction energy with 30-40 % of water content. It means that the gypsum material can be used as selected fill material because it fulfils its requirement where IP10%.

The pros and cons of using calcium lignosulfonate as a recycled anti-aging additive on engineering properties of bituminous mastics

High temperature and traffic loading are two primary threats for asphalt pavement during the pavement's life cycle. The mentioned threats lead to significant distractions, namely bitumen's oxidative aging, rutting, and fatigue failure. In this study, calcium lignosulfonate (CLS) obtained from lignin was investigated as an anti-aging bitumen additive. After morphology analysis of CLS particles based on field emission scanning electron microscopy (FESEM) technique, the CLS was mixed with the bitumen of 60/70 penetration grade at four quantities (i.e., 5%, 10%, 15%, and 20%). Then, the rolling thin film oven test (RTFOT) was used to simulate bitumen aging. In the next step, physical tests (penetration, softening point, and ductility), rheological tests (rotational viscosity and dynamic shear rheometer), and performance tests (multiple stress creep recovery and linear amplitude sweep) were conducted on both aged and un-aged samples. Finally, to evaluate the change of bitumen's chemical components during the aging process, the Fourier transform infrared spectroscopy (FTIR) was carried out. Results showed that CLS particles had a bumpy structure. Moreover, the addition of CLS into the bitumen increased the stiffness and high-temperature performance of bitumen. Although CLS modified bitumen needed more energy for mixing and compaction to compare with virgin bitumen, CLS modified bitumen had lower rutting susceptibility than virgin one. The presence of CLS within the bitumen increased the binder's brittleness, leading to fatigue life degradation. Based on FTIR analysis and aging indices, CLS as a recycled bitumen additive can significantly inhibit bitumen's oxidative reaction.

A new method for increasing the density of modulated sandy soils by using cement dust

This research is an empirical method for estimating the possibility of using cement dust as an additive for sandy soil during the field compaction process. The soil samples were brought from Al-Najaf city and treated with cement dust .Twenty test models were prepared and compacted in the standard and modified mould of Proctor test. These models were divided into two broad series, firstly consisted of ten soil samples, five from these samples were carried out at constant compactive energy (E=355.5 kJ/m3) for cement dust (4 , 8, 12 and 16%) in addition to one case with no cement dust. This energy is less than standard Proctor test energy. Another retained models were tested with compactive energy equal to the energy of standard Proctor test (E=592.5 kJ/m3) for the same percentage cement dust. The second series of models were involved ten models, five samples compacted at energy corresponding to Modified Proctor Test (E=1197.03 kJ/m3) and other retained models at compactive energy higher than compactive energy of the modified Proctor test (E=2681.4 kJ/m3). The results of laboratory tests which carried out on selected soil showed with increasing compactive energy, the optimum cement dust decreased (this percent was corresponding to the peak dry density in the laboratory) . In other words, the optimum cement dust percents were equal to (4%), (6.6%), (8%) and (12%) for compactive energy (E=355.5, 592.5, 1197.03 and 2681.4 kJ/m3) respectively, and the addition of these percents of cement dust leaded to increase in the maximum dry density (4%, 5.3%, 17.1% and 20.5%) for compactive energy (E=355.5, 592.5, 1197.03 and 2681.4 kJ/m3) respectively.

Durability evaluation of easy compaction and high-durability ultra-thin overlay

As one of the most popular preventive maintenance of road surface, the ultra-thin overlay with good durability and surface function could provide better conditions for the safe and smooth running of vehicles. The objective of this study is to prepare an ultra-thin overlay with easy compaction and high-durability (ECHD) and to evaluate its durability. First, the optimal dosage of the easy compaction modifier was determined based on the grey theory. Then, matrix asphalt and SBS-modified asphalt mixtures were used as control groups. Through an experimental design, the ease of compaction, fatigue durability, ageing resistance, surface function durability, and interlayer durability of the three asphalt mixtures were compared. Finally, using the test road, a field effect evaluation of the durability of the ECHD ultra-thin overlay was performed, and a durability evaluation system for ultra-thin overlays was established. The results showed that the optimal content of the modifier was 6%. The ECHD asphalt mixture exhibited the smallest Compaction energy index (CEI), largest compaction rate (K), and easiest compaction. The splitting strength ratio was used as the ageing coefficient to evaluate the ageing performance. Compared with the matrix asphalt and SBS-modified asphalt mixture, the ECHD asphalt mixture exhibited better ageing durability and fatigue durability. Moreover, after 30,000 wear times, the mass loss rate of ECHD ultra-thin overlay was 0.4%, the texture depth and pendulum value decreased by 25% and 16%, and the shear strength and pull-off strength decreased by 6% and 20% respectively, which showed that it had the best performance in wear-resistance, skid-resistance, water-impermeable and interlayer durability. In addition, the durability effect of the ECHD ultra-thin overlay test road was evaluated and a durability evaluation system of the ECHD ultra-thin overlay was proposed, which can act as a reference for the durability evaluation of the same type of overlays.

Suitability of Shale Treated with Palm Kernel Shell Ash and Pulverized Palm Kernel Shell As Landfill Liners at Nguzu Edda, Southeastern Nigeria

Wastes are mostly disposed of in landfills, which pose threat to soil and groundwater as a result of percolation of leachate. Therefore, barrier soils are required for the lining of a landfill to prevent seepage of leachate into the surrounding groundwater system. In this regard, the suitability of ten shale samples treated with 0-12 % (increments of 2 %) proportion of palm kernel shell ash (PKSA) and pulverized palm kernel shell (PPKS) by dry weight of the shale samples were evaluated for uses as landfill liner. The samples were subjected to series of geotechnical tests to determine the index properties, and strength characteristics of the natural and treated shale using West African standard (WAS) and Modified AASHTO (MAS) compactive energy levels for comparison purposes. The shale was classified as A-7-5. The atterberg limits test results show that liquid and plastic limits generally decreased, while the plasticity index (PI) increased with increase in PKSA and PPKS contents. The results also demonstrated that maximum dry density (MDD), volumetric shrinkage strain (VSS) and hydraulic conductivity decreases significantly while optimum moisture content (OMC) increases with increase in PKSA and PPKS contents for the both energy levels. The maximum strength of 380.30 and 448.70 KPa were recorded at 4 % of the stabilizers. The findings affirmed that the samples met the requirements for landfills liner, although PPKS was more effective than PKSA for both energy levels. Moreover, the addition of PKSA and PPKS to liners can also be an alternative means of its disposal.

Modeling the Compaction Characteristics of Fine-Grained Soils Blended with Tire-Derived Aggregates

This study aims at modeling the compaction characteristics of fine-grained soils blended with sand-sized (0.075–4.75 mm) recycled tire-derived aggregates (TDAs). Model development and calibration were performed using a large and diverse database of 100 soil–TDA compaction tests (with the TDA-to-soil dry mass ratio ≤ 30%) assembled from the literature. Following a comprehensive statistical analysis, it is demonstrated that the optimum moisture content (OMC) and maximum dry unit weight (MDUW) for soil–TDA blends (across different soil types, TDA particle sizes and compaction energy levels) can be expressed as universal power functions of the OMC and MDUW of the unamended soil, along with the soil to soil–TDA specific gravity ratio. Employing the Bland–Altman analysis, the 95% upper and lower (water content) agreement limits between the predicted and measured OMC values were, respectively, obtained as +1.09% and −1.23%, both of which can be considered negligible for practical applications. For the MDUW predictions, these limits were calculated as +0.67 and −0.71 kN/m3, which (like the OMC) can be deemed acceptable for prediction purposes. Having established the OMC and MDUW of the unamended fine-grained soil, the empirical models proposed in this study offer a practical procedure towards predicting the compaction characteristics of the soil–TDA blends without the hurdles of performing separate laboratory compaction tests, and thus can be employed in practice for preliminary design assessments and/or soil–TDA optimization studies.

Soil stiffness as a function of dry density and the degree of saturation for compaction control

A data set of the coefficient of vertical subgrade reaction for a plate diameter of 30 cm, KP.FWD, measured by Portable Falling Weight Deflectometer tests in full-scale compaction tests on sandy soil using various types of compaction machines was analysed. Based on this analysis and the previous analysis of a CBR data set from another full-scale compaction test series, a set of conclusions could be drawn. The soil stiffness indexes (SSIs), CBR and KP.FWD, can be expressed by, respectively, an empirical equation multiplying a function of ρd and another of Sr, where CBR and KP.FWD decrease significantly as Sr increases. As such, ρd values cannot be estimated from SSI alone. By fixing the field ρd – w compaction curve by keeping the soil type and the field compaction energy level, CELf, to those in the field compaction tests in which the SSI – ρd – Sr correlation has been calibrated, field compacted ρd &w states can be estimated by measuring the SSI values. Then, by the upper-bound and lower-bound control of SSI, the field compacted states approach the specified target, where, typically, ρd = the maximum dry density for CELf and Sr = the optimum degree of saturation, (Sr)opt. A method to incorporate this indirect but fast SSI-based compaction control into the conventional ρd &w-based compaction control is proposed.

Use of Granulated Rubber Tyre Waste as Lightweight Backfill Material for Retaining Walls

The use of industrial waste in civil engineering applications constitutes a potential innovative effort to reduce environmental degradation and enable a sustainable use of natural resources. This paper reports a comprehensive laboratory study that was performed to evaluate the rubber granulates from End-of-Life Tyres (ELTs) as a lightweight backfill material in retaining walls. Various tests have been performed to provide specific information on the mechanical and physical properties of a detailed range of particle sizes smaller than 12 mm, with six different particle size distributions (S1: 0.0–0.8 mm/S2: 0.6–2.0 mm/S3: 2.0–4.0 mm/S4: 2.0–7.0 mm/S5: 90% 2.0–7.0 mm + 10% 0.6–2.0 mm/S6: 50% 2.0–7.0 mm + 50% 0.6–2.0 mm). The density and unit weight, compaction energy, compressibility, shear strength, and deformability have been evaluated to determine their performance. As a main conclusion, the research confirms that rubber granulates from ELTs possess great potential as backfill material behind retaining walls. The characteristic values of the geotechnical parameters have been estimated according to Eurocode 7. The friction angle results range from 18.27 to 23.21 degrees, and the cohesion results are wide-ranging, with values from 9.35 to 17.83 kPa. For this reason, two cantilever L-shaped retaining walls, selected as representative case studies, have been tested with these sample properties. The results of the geotechnical verifications are presented together with a comparison of the safety factors in accordance with the Spanish standard design (CTE-DB-SE-C) and the European (EC7-1) regulations. The calculations indicate that the overdesign factors (ODF) achieved in the verifications using the material properties of the S4, S5, and S6 combination improve the calculation results obtained if a conventional filler material such as sand is considered.

Performance evaluation and sustainability assessment of precast concrete paver blocks containing coarse and fine RAP fractions: A comprehensive comparative study

Concrete paver blocks have recently developed as the most attractive and economically viable option for extensively recycling wastes. This deescalates the environmental concerns related to waste disposal, encourages conservation of natural resources, and contributes to a sustainable production process. In the present study, laboratory performance of concrete paver blocks using coarse and fine fractions of non-beneficiated reclaimed asphalt pavement (RAP) materials, derived as a waste residue from demolished asphalt pavement, was comprehensively and comparatively investigated. A two-factor analysis of variance and multiple comparisons test was performed to investigate the influence of RAP proportion and moist curing age. The laboratory findings revealed that the produced concrete blocks containing RAP have a great potential to be used for medium, heavy, and very-heavy traffic applications. The dosage of RAP as a natural aggregate replacement as well as the durability of RAP concrete can be increased using a staged mixing approach and a time-controlled dual-source compaction technique, which involves synchronized impact pressure and vibratory compaction energy. Moreover, assessing economic and environmental benefits highlighted the potentially sustainable aspects of recycling RAP fractions into precast concrete paver blocks.

Evaluating the performance of sonic and ultrasonic tests for the inspection of rammed earth constructions

There are many examples of historical rammed earth constructions for which the development of valid methods for evaluation of their conservation state is a major concern for conservation agencies of all around the world. On the other hand, rammed earth is attracting the attention of modern architecture trends because of its outstanding performance from an ecological perspective. Thus, the development of reliable non-destructive tests for the inspection of new and existing rammed constructions is of major interest. Ultrasonic and sonic tests are among the most commonly used. While the former has been the subject of numerous studies in rammed earth soil, sonic tests still requires further experimental development. In general, both tests demand a more precise study of their performance according to different states of loading and damage to evaluate the state of structural degradation. Additionally, the procedure commonly used to apply both tests need to be revised in order to provide a more reliable and precise assessment of the time-of-flight of elastic waves. Therefore, on the one hand, this paper evaluates and compares the sensitivity of both non-destructive inspection techniques to different levels of damage induced on the tested samples and possible heterogeneous properties such as compaction energy distribution during the manufacturing process. On the other hand, an automated procedure for the analysis of the experimental recordings and the identification of the time-of-flight of sonic and ultrasonic waves is developed to facilitate the applicability of these techniques. This new procedure consists of a simple signal analysis algorithm that avoids the time-consuming task of manual inspection of the signals and reduces uncertainty in the final results. The results show that sonic test is a valid a promising tool for the inspection of this type of constructions. It performs better than ultrasonic test, which could also be used in practice with some limitations.

Experimental Study on Consolidation Characteristics of Compacted Loess

The prediction of foundation settlement is an important topic in loess filling engineering. Based on a filled foundation in Yan’an, China, this study explores the consolidation characteristics of compacted loess with different compaction energy and consolidation pressure through consolidation tests, analyzes the strain-time curve and refines the curve within 2 h, separates the primary and secondary consolidations, and obtains the critical time point between the primary and secondary consolidations. Deformation rate S t ′ and cumulative deformation St were introduced to analyze the S t ′ − St curve at the secondary consolidation stage; the secondary consolidation coefficient was employed to describe the secondary consolidation characteristics of compacted loess. According to the secondary consolidation characteristics, a prediction model of loess settlement considering different compaction energy and fill thickness was proposed, and the applicability of the model was further analyzed. The model will facilitate in guiding the design and construction of loess filling engineering.

Effect of compaction energy on grain breakage of CDW, local soil and soil-CDW mixtures

ABSTRACT The use of construction and demolition wastes (CDW) as alternative material in engineering has proved promising applications, especially in pavement layers. However, the high grain breakage of this material has led to uncertainties regarding its performance. The present study assessed the effect of compaction energy on grain breakage of CDW, comparatively to a local sandy-clay (SC) soil with gravels, and mixtures of soil-CDW. Other geotechnical properties were also evaluated for application in pavements. Results showed the feasibility of using CDW as pavement layer material when compacted using modified energy. The local sandy-clay soil was not appropriate for pavement layers, while soil-CDW mixture improved soil geotechnical characteristics, allowing its use as subbase course. Grain breakage analysis, based on a statistical approach, showed that CDW undergoes greater particle size distribution change, not altered by compaction energy increase. Results confirmed that soil-CDW mixture presented superior performance for pavement layers.

Analysis of Soil Compaction using Proctor Standards in Highway Construction Design

Soil is an essential structural material since it must be able to support the load applied, which is why soil must have sufficient bearing ability. The dry density affects the strength and deformation parameters. To achieve stable soil and meet the technological specifications for building a foundation, good embankment condition necessitates compaction. In this analysis, the updated proctor method was compared to the soil compaction energy proctor test method. Compaction energy is a crucial factor in assessing the soil’s intensity, and it must be taken into account during the planning stage. The laboratory’s Standard Proctor density was 1.63 gr/cm3, and the modified proctor density was 2.18 gr/cm3, according to the findings of this report. The outcome of the soil density sand cone test indicates that the degree of soil density is 97.31 percent for the standard proctor test process, indicating that the soil density has been achieved and the soil embankment should be used, but as applied to the soil density in the laboratory by standard proctor test, the degree of soil density is 73.54 percent lower.

EXPERIMENT REGARDING MONTMORILLONITE CONTENT AND STRENGTH PROPERTIES IN BENTONITE UNDER THE INFLUENCE OF HEAT

At present, underground geological disposal at depths greater than 300 m is considered a viable disposal option for high-level radioactive waste generated from the reprocessing of spent fuel used in nuclear power plants. According to the Japan Nuclear Cycle Development Institute [1] and Agency for Natural Resources and Energy [2], in geological disposal, bentonite is employed as the primary component of buffer material to fill gaps between waste and geologic rock. However, specification details have yet to be completely determined. It is anticipated that the buffer material will be exposed to high temperature due to the heat generated by the vitrified solid. This study aims to understand the mechanical properties of bentonite buffer material by employing uniaxial compression tests with temperatures between 30°C to 90°C applied to bentonite specimens having received a temperature history treatment of 200°C applied over six months. Results show that the maximum compressive strength of the sample given the temperature history is lower than that of the sample without the temperature history. Furthermore, the montmorillonite content of the sample given a temperature history of 200°C also decreased. The reason for the decrease in strength seems to be that the compaction energy during fabrication decreased due to the decrease in the montmorillonite content. This is because the specimens were fabricated so that the dry density was constant. It seems that the maximum compressive stress decreased with increasing temperature regardless of temperature history. The reason for this seems to be microcracks, which appear to decrease rigidity and, therefore, compressive strength.

Achieving Ultra-High Performance Concrete by Using Packing Models in Combination with Nanoadditives.

This paper describes the packing models that are fundamental for the design of ultra-high-performance concrete (UHPC) and their evolution. They are divided into two large groups: continuous and discrete models. The latter are those that provide the best method for achieving an adequate simulation of the packing of the particles up to nanometric size. This includes the interaction among the particles by means of loosening and wall coefficients, allowing a simulation of the virtual and real compactness of such particles. In addition, a relationship between virtual and real compactness is obtained through the compaction index, which may simulate the energy of compaction so that the particles are placed in the mold. The use of last-generation additives allows such models to be implemented with water–cement (w/c) ratios close to 0.18. However, the premise of maximum packing as a basic pillar for the production of UHPC should not be the only one. The cement hydration process affected by nanoadditives and the ensuing effectiveness of the properties in both fresh and hardened states according to the respective percentages in the mixture should also be studied. The characterization tests of the aggregates and additions (dry and wet compactness, granulometry, density and absorption) have been carried out in order to implement them numerically in the polydisperse packing model to obtain the compactness of the mixture. Establishing fixed percentages of nanoadditives in the calculation of the mixture’s compactness. The adequate ratio and proportion of these additions can lead to better results even at lower levels of compactness. The compressive strength values obtained at seven days are directly proportional to the calculated compactness. However, at the age of 28 days, better results were obtained in mixes with lower cement contents, fewer additions and lower compactness. Thus, mixes with lower cement contents and additions (silica fume and limestone filler) with a compactness of φ = 0.775 reached 80.1 MPa of strength at 7 days, which is lower than mixes with higher cement contents and number of additions (SF, limestone filler and nanosilica), which achieved a compactness of φ = 0.789 and 93.7 MPa for compressive strength. However, at 28 days the result was reversed with compressive strengths of 124.6 and 121.7 MPa, respectively.

Effect of waste PET and CR as sand replacement on the durability and acoustical properties of semi dense asphalt (SDA) mixtures

Construction materials research is consistently striving to improve sustainability, in the reduction of virgin materials by use of otherwise landfilled materials of the same purpose. Crumb rubber (CR) from end-of-life tires and polyethylene terephthalate (PET) from post-consumer liquid containers are two of the most commonly circulating forms of waste in the urban environment. This study investigated the replacement of semi-dense asphalt (SDA) sand by untreated mechanically shredded CR and PET, at 2.5 and 5.1% respectively by total mass of aggregates. The mixtures were evaluated by compactability, indirect tensile strength (ITS), fracture energy (FE), water sensitivity by ITS ratio (ITSR%), surface texture and acoustic absorption tests. After compaction, the CR and PET samples experienced an elastic rebound effect, which resulted in the air voids being higher than expected. Also, the PET samples required more compaction energy. The ITS, FE and ITSR% were significantly reduced with CR replacement, while the PET mixture performed similar to the control, especially in FE. The sound absorption was related more to the air voids than the material type, although the absorption coefficients of the SDA was not found to be significant. The CR reduced the texture level of the pavement significantly in comparison to the control, while texture level remained the same for the PET mixture, despite a difference in the porosity. Further studies were performed using a mixture replacing PET by aggregate volume at 5.1%, comparing it to the control SDA in terms of low temperature cracking and permanent deformation at 50 °C. While the compactability of the PET mixture was now similar to that of the control, the resistance to cracking and permanent deformation was lower. Although the PET mixture had some interesting ductility properties, the replacement of sand by CR and PET is not recommended, and the more common use as asphalt mixture modifiers with fairly low addition contents of around 1% is more sound.