Pavement Subbase Research Articles

Re-cementation of Recycled Concrete Aggregate in Pavement Base or Sub-base

Recycled concrete aggregate (RCA) is often used as a pavement base or sub-base material. One unique concern of RCA used for such purposes is re-cementation. Although re-cementation increases the stiffness and bearing capacity of RCA, it may induce cracking if RCA becomes bound or partially bound. Four approaches were used in this study to investigate RCA re-cementation in pavement sub-base, including long-term monitoring of a trial site, test of RCA samples retrieved from the site, performance simulation based on mechanistic-empirical pavement design guide (ME-PDG), and numerical analysis. The trial site reveals that RCA becomes partially bound after 11 years of road use. The bound material exhibits properties similar to those of cement-treated base (CTB). However, due to variations in the content and composition of fines in RCA, the extent of re-cementation is not uniform in sub-base. According to the analysis results generated by ME-PDG, reflective cracking occurs if RCA is assumed to be CTB. Conversely, if bound RCA is non-monolithic, it may not have significantly negative effect on pavement performance. The fine content or composition of fines in RCA may be specified to further reduce the risk of RCA re-cementation.

THE GEOTECHNICAL PROPERTIES OF RECYCLED CONCRETE AGGREGATE WITH ADDITION OF RUBBER CHIPS DURING CYCLIC LOADING

The following paper presents the results of tests performed on the reclaimed waste, namely the Recycled Concrete Aggregate (RCA). Geotechnical study was undertaken, in order to obtain physical and mechanical properties of RCA improved with rubber grains. Such a mix could exhibit increased elastic strain development during load cycles, which are typical for traffic. For better understanding of its exceptional behaviour under repeated loading, cyclic CBR tests were conducted in various stages of loading. For the purpose of bearing capacity analysis, uniaxial test was also conducted. While the cyclic loading and mechanical stabilization are a cause of aggregates crushing, another particle size distribution could occur and may not fulfil quality requirements. Determination of resilient modulus Mr on the basis of a repeated loading test and development of displacements during the tests have also been presented. The Mr value for pure RCA was equal to 495.6MPa. The addition of rubber chips in amount 0.5% and 1% results in rise of resilient modulus value, equal to 632.4MPa and 698.0MPa respectively. During the tests the plastic strain abate was recognised. The plastic displacement analysis shows increase of the permanent settlement due to cyclic loading in case of 0% and 1% rubber chips content. The 0.5% rubber chips addition results in smaller plastic displacement. The plastic and elastic displacement was later analysed in order to characterize the deformation behaviour of RCA. The paper proposes also a possible guideline for using the RCA mix as a material in pavement subbase construction.

Developing statistical limits for using the light weight deflectometer in pavement construction quality assurance

Traditional methods of evaluating the quality of pavement subbase and subgrade compaction require considerable time and resources. Therefore, agencies continue to seek and evaluate safe, reliable, rapid, and cost-effective alternatives for quality assurance of the field compaction of unbound pavement layers. The light weight deflectometer (LWD) is a promising alternative that is increasingly gaining attention. This study investigated the feasibility of developing statistical limits for the compaction of specified combinations of subbase and subgrade materials in terms of their LWD maximum allowable deflections (MAD), to replace the need for site-specific LWD limits derived from the onsite test sections. Statistical limits were developed for six common subgrade and subgrade–subbase combinations used for highway pavement construction: lime-modified, cement-modified, and natural subgrade and the first six-inch lift of Number 53 crushed stone subbase overlaying these subgrades. Two sources of data, test sections and acceptance tests, were used. For a given material type, the data from the former exhibited less variability between projects. The test section data yielded MADs that did not vary significantly between projects for cement- and lime-modified subgrade, non-modified subgrade, and six inches of Nr.53 crushed stone over lime-modified subgrade.

Increasing the reaction kinetics of alkali-activated fly ash binders for stabilisation of a silty sand pavement sub-base

The paper addresses several options to improve the reaction kinetics of alkali-activated low-calcium fly ash binders for soil stabilisation in road platforms. For that purpose, an experimental programme was established to assess the strength evolution, with time, of different binders, based on ash, lime, sodium chloride and alkali solutions, applied in the stabilisation of a silty sand. The tests included unconfined compression strength tests, triaxial tests and seismic wave measurements performed at different curing periods. The results were compared with a binder made of Portland cement and a commercial additive specifically designed for soil stabilisation in road applications. The activated ash mixtures with lime were the most performing producing a significant increase in the reactions development and, consequently, in the strength gain rate. The sodium chloride significantly improved the lime and lime-ash mixtures, but provided only a slight improvement in the activated ash mixtures.

Strength Characterization of Stabilized A-5(10), A-7-5(16), A-4(3) and A-2-7(1) Laterite Soils Individually Using Supaset Cement

The purpose of this research work is on the strength characterization of the Supaset Portland cement stabilized with laterite soil materials from four different borrow pits locations within Southwest part of Nigeria and the level of their usefulness for highway pavement subbase and basecourse. The four laterite soils after laboratory experiments are classified as A-5(10) silty soil; A-7-5(16) clayey soil; A-4(3) silty soil and A-2-7(1) clayey gravely sandy soil respectively. Stabilization of each laterite soil with the cement at percentages of 0% through 14% at the interval of 2% shows that with the increase in cement content during stabilization process the optimum moisture content of each soil specimen is reducing while the related maximum dry density is increasing. Furthermore, while considering at natural and stabilized states, both unsoaked and soaked California Bearing Ratio, uncured and unconfined compression strengths values of the tested specimens are increasing with increase in cement content with soil A-4(3) having the highest value while soil A-5(10), A-2-7(1) and A-7-5(16) values followed respectively. The coefficient of permeability of each soil specimen stabilized was reducing as the cement content was increasing. The chemical composition tests on Supaset Portland cement revealed CaO and SiO2 are the major components while for those of soils are SiO2 and Al2O3. The significance of this study is that although A-5(10) and A-4(3) silty soils stabilized by Supaset Portland cement of grade 32.5R attained the 750 kN/m2 minimum standard strength requirement for subbase, A-7-5(16) and A-2-7(1) clayey soils did not satisfy same. The justification for this research is that Supaset Portland cement is an economical and valuable material to stabilize silty soils but not cost-effective for the stabilization of clayey soils for highway pavement in order to prevent its incessant and premature failure.

Environmental impacts of utilizing waste steel slag aggregates as recycled road construction materials

Slag is an industrial waste generated during the steelmaking process. Electric arc furnace slag (EAFS) and ladle furnace slag (LFS) are both produced at different stages of steelmaking process, respectively, in electric arc furnaces and refining ladle furnaces. As part of this research, an extensive suite of engineering and environmental tests were undertaken on steel slag aggregates to evaluate their potential usage as road construction materials. The engineering assessment included particle size distribution, hydrometer, organic content, flakiness index, Atterberg limits, particle density, water absorption, pH, minimum and maximum dry densities with a vibrating table, modified compaction, California bearing ratio (CBR) and Los Angeles abrasion tests. In addition, a suite of environmental tests comprising total and leachable heavy metal tests were undertaken on both types of steel slag aggregates. From an environmental perspective, EAFS and LFS were found to pose no environmental risks for use as aggregates in roadwork applications. The engineering properties of LFS aggregates with its satisfactory geotechnical and environmental results, particularly its high CBR values, indicated that the material was ideal for usage as a construction material in roadwork applications such as pavement base/subbases and engineering fills. EAFS, with its comparatively lower CBR value, was found to be only suitable to use as a construction material for pavement subbases and engineering fills. The usage of steel slag aggregates in roadwork applications would bring about a practical end-of-life alternative for their sustainable reuse and possibly divert large amount of these waste materials from landfills.

Influences of various construction and demolition materials on the behavior of a clay

Construction and demolition (C&D) waste materials, which are environmental and financial problems, increase with continuous urbanization and industrialization. The C&D waste materials can be recycled and used as a material for new engineering applications. This study focuses on usage of the crushed brick, dragged asphalt, and crushed concrete paving slab aggregates with clay in pavement subbases. In this research, an intensive series of California Bearing Ratio (CBR), compaction, unconfined compressive strength (UCS), and swelling tests were carried out on the clay with various C&D waste materials. The performance of the implementation was investigated with the clay only, C&D materials only, and clay with C&D materials at the mix ratios of 5, 10, 15, 20 % by dry weight. The testing results showed a maximum of 13, 37, and 30 % increase in the CBR values of the mixtures with 20 % content of dragged asphalt, crushed brick, and crushed concrete paving slab of C&D waste materials, respectively. Compaction tests resulted in decrease in optimum moisture content (wopt) regardless of type of C&D materials, while maximum dry unit weight (γdrymax) changed based on the materials type. Performed UCS tests revealed that there has been an increase in strength of the mixtures as the amount of any C&D waste material increased in the mixture. Also, swelling percentage of the clay was found to decrease with an increase in the amount of any C&D waste material.

Salts accelerating strength increase of coal fly ash–carbide lime compacted blends

Compacted coal fly ash–carbide lime (two industrial by-products) blends have great potential application in geotechnical earthworks such as sub-base and base of pavements, beds of pipelines and spread footings, embankments and in erosion control. Pozzolanic reactions occur between silica and alumina in amorphous phases (found in the fly ash) and Ca2+ (existent in carbide lime) in an alkaline environment. However, pozzolanic reactions are notoriously slow at ambient temperatures, requiring long curing periods for certain applications. Therefore, this study aims to verify the influence of application of distinct salts [sodium chloride (NaCl), magnesium oxide and potassium permanganate] in the acceleration of unconfined compressive strength (qu) increase of coal fly ash–carbide lime blends. Results have shown that small amounts of certain salts allowed to accelerate qu increase of coal fly ash–carbide lime blends. Among the studied salts, sodium chloride presented the best results after 28 days of curing. Coincidently, sodium chloride is also relatively cheap and of great availability, making it convenient for extensive use.

CONTRIBUCIÓN AL MEJORAMIENTO DE LAS CALLES DE LA CIUDAD DE PORTOVIEJO MEDIANTE LA CONSTRUCCIÓN DE BASES Y SUBBASES TRATADAS CON EMULSIONES ASFÁLTICAS

Abstract: The subbase and base materials of flexible road pavements traditionally used in Canton Portoviejo are not agglomerated, classified as well-graded stone aggregates, and in some cases with high plasticity. These materials are sometimes not behave properly under the influence of the loads and the presence of moisture. Currently internationally layers for pavement, various additives which improve their performance are used, among which are asphalt emulsions. The work is a study of the influence of the use of asphalt emulsion as a binder of these materials, as well as the most appropriate to use percentages. It is an alternative for engineers as a contribution to the improvement of pavements within our region and a contribution to improving the quality of life of our people.
 Index Terms: Asphalt emulsions, gravel-emulsion, bases, subbases, treated bases

Stabilisation of dune sand using electric arc furnace dust

Dune sand is one of the predominant soils in the world, particularly in the Arabian Peninsula and North Africa. In order to use these soils in constructions, pre-treatment of sand is essential. Though the usage of cement for stabilising sand has long been the practice to achieve the required strength, it is not cost effective and its manufacturing consumes a lot of energy. Consequently, it would be noble to use industrial by-products, often considered as waste materials, such as electric arc furnace dust (EAFD), in the stabilisation of sand. This research reports the potentiality of using EAFD for improving the strength of dune sand. Specimens, mixed with 2% cement and mixed with 5, 10, 20 and 30% EAFD plus 2% cement, were evaluated using unconfined compressive strength, soaked CBR and durability tests. Results of this investigation indicated that dune sand stabilised with 20 and 30% EAFD plus 2% cement has been qualified as a construction material for sub-base in rigid and flexible pavements, respectively, as per ACI requirements. Scanning electron microscope, energy dispersive X-ray analysis and backscattered electron images, in addition to, XRD analysis were used to identify the various phases in the sand-2% cement-30% EAFD mixture.

Performance of cement-stabilised crushed brick aggregates in asphalt pavement base and subbase applications

Demolished brick is one of the main components of construction waste, and its recycling for use in asphalt pavement base and subbase is a relatively new technique. This work studies the performance of cement-stabilised crushed brick aggregates (CSCBA) and proves the applicability of crushed brick aggregates (CBA) in asphalt pavement base. A scanning electron microscope (SEM), X-ray diffractometer (XRD) and Fourier infrared spectrum (FIS) were used to investigate the micro performance of CBA. Six types of CSCBA were designed with the following CBA contents: 0%, 20%, 40%, 60%, 80% and 100%. The properties of CSCBA were investigated, including compaction properties, compressive strength, split strength, compressive resilient modulus, shrinkage performance and fatigue performance. SEM was also used to analyse the strengthening mechanism of CSCBA. This study's results are useful for engineering practice, particularly for identifying (a) the properties of CSCBA and (b) the upper limits of CBA applicability for asphalt pavement base and subbase for low-grade highway.

The use of non-conventional materials in asphalt pavements base

In Brazil's Middle West Region, there is a scarcity of granular natural material to be used in subbase and base layers of urban asphalt pavements. As most urban roads to be paved have a low volume of traffic, it becomes necessary to define alternatives for the pavements’ construction that have technical and economic feasibility. In this paper, laboratory studies were conducted with traditional and non-traditional materials available in the region, such as superficial fine soil found in abundance, crushed rock, quarry waste, hydrated lime and gravel. With the mixtures that showed better results in the laboratory, an experimental asphalt pavement was constructed to evaluate the performance of the structure made with different materials. During construction and after two years, the pavement was monitored by field tests. The results showed that the studied mixtures present technical feasibility and can be used in substitution for materials traditionally used.

Simulation of Shakedown Behavior in Pavement’s Granular Layer

While in the design of flexible pavement the significance of asphalt layers is understood, the role of granular layers supporting the asphalt layers should not be underestimated. The behavior of granular layers used in base, sub-base or subgrade layer of flexible pavement is complicated due to nonlinear elastoplastic response of materials subjected to dynamic load of traffic. Shakedown theory integrated with Mohr-Coulomb criterion is applied to simulate the response of granular layers to dynamic loading in a numerical analysis. The results of analysis is then compared to simple the results of modeling without considering shakedown effects and the conclusion is drawn.

Engineering and Environmental Assessment of Recycled Construction and Demolition Materials Used with Geotextile for Permeable Pavements

This paper describes laboratory testing to investigate the suitability of recycled construction and demolition (C&D) materials as alternative subbase materials for permeable pavements. Permeable pavements are increasingly being used as urban stormwater management systems. Three commonly found recycled C&D waste materials, crushed brick (CB), recycled concrete aggregate (RCA), and reclaimed asphalt pavement (RAP), were investigated to assess their suitability as permeable pavement subbase materials. Geotextile was also used in this research to trap pollutants. The laboratory tests included basic physical characterization such as particle size distribution, specific gravity, water absorption, Los Angeles abrasion, California Bearing Ratio (CBR), and modified Proctor compaction tests. In addition, hydraulic conductivity tests were undertaken in a laboratory test setup with different influent suspension percentages and moisture contents. Temporal variations of effluent suspension percentages were investigated to assess clogging effects. It was found that the geotextile layer did not have any effect in terms of permeability of the C&D materials. The chemical assessment included organic content, pH value, trace element, and leachate concentration for a range of contaminant constituents and compared with maximum allowable limits in soil and natural water as well as with the environmental protection authorities' requirements. In terms of geotechnical and chemical assessment for permeable pavement applications, RCA was found to be a suitable alternative construction material for permeable pavements, while CB was borderline and RAP did not meet some of the specified requirements.

Self-cementing properties of recycled concrete aggregates (RCA) on the example of tests of material and layers of pavement subbase

The work is an attempt to summarize the experience concerning the diagnosis of the practical properties of recycled aggregate concrete cement (RCA). It describes the phenomenon of self-cementing properties which was investigated in both the laboratory and on field tests including compressive strength of RCA, non-conventional oedometric tests of RCA and plate bearing tests on the surface of RCA layer. The described self-cementing properties were remarked, however, the RCA material was characterized by smaller increase in the value of parameter EV2 in a 2-year period of time than recycled concrete materials described in the available literature.

Laboratory evaluation of cement treated aggregate containing crushed clay brick

Abstract: The waste clay bricks from debris of buildings were evaluated through lab tests as environmental friendly materials for pavement sub-base in the research. Five sets of coarse aggregates which contained 0, 25%, 50%, 75% and 100% crushed bricks, respectively, were blended with sand and treated by 5% cement. The test results indicated that cement treated aggregate which contains crushed clay brick aggregate had a lower maximum dry density (MDD) and a higher optimum moisture content (OMC). Moreover, the unconfined compressive strength (UCS), resilience modulus, splitting strength, and frost resistance performance of the specimens decreased with increase of the amount of crushed clay brick aggregate. On the other hand, it can be observed that the use of crushed clay brick in the mixture decreased the dry shrinkage strain of the specimens. Compared with the asphalt pavement design specifications of China, the results imply that the substitution rate of natural aggregate with crushed clay brick aggregate in the cement treated aggregate sub-base material should be less than 50% (5% cement content in the mixture). Furthermore, it needs to be noted that the cement treated aggregate which contains crushed clay bricks should be cautiously used in the cold region due to its insufficient frost resistance performance.

도로기층 보조재로서의 폐주물사 안정화에 관한 연구

도로기층 보조재로서의 폐주물사 안정화에 관한 연구

Flexural beam fatigue strength evaluation of crushed brick as a supplementary material in cement stabilized recycled concrete aggregates

In recent years, efforts have been made by various researchers to explore the sustainable use of Construction and Demolition (C&D) materials as a construction material in civil engineering applications. Recycled crushed brick is a commonly found material from demolition activities and works to date on this material in pavement applications have been limited to its usage in unbound pavement layers. This research was undertaken to evaluate the performance of crushed brick as a supplementary material in cement stabilized recycled concrete aggregates. An extensive suite of tests were undertaken on the crushed brick and recycled concrete aggregate blends stabilized with 3% cement. The laboratory evaluation comprised pH, plasticity index, foreign materials content, particle size distribution, linear shrinkage, California Bearing Ratio, modified Proctor compaction, Repeated Load Triaxial test, Unconfined Compressive Strength Test and Flexural Beam Tests. The cement stabilized blends with up to 50% crushed brick content and 3% cement were found to have physical properties, which comply with the local state road authority requirements. The results of Repeated Load Triaxial tests indicated the Recycled Crushed Aggregate/Crushed Brick (RCA/CB) blends performed well with 50% Crushed Brick (CB) content just on the border line for bound pavement material. Unconfined Compression Strengths met the minimum requirement for 7days of curing for all blends, while the 28 day strength of the blends also improved significantly. The results of the flexural beam tests were noted to be consistent with past works with cement stabilized quarry produced crushed rock products. The modulus of rupture and flexural modulus for all the cement-stabilized blends were found to be consistent with the previous works, which indicate that these blends are suitable for applications such as cement-stabilized pavement subbases. The fatigue life was also within the range that has been previously reported for quarry materials. The cement-stabilized blends with crushed brick as a supplementary material with up to 50% brick content and 3% cement were found to have physical and strength properties, which would comply with road authority requirements.

Use of wastewater sludge for base and subbase of road pavements

The occurrence and destination of wastewater sludge in the soil and hydric resources has been recognized as an emerging issue in preserving the environment. This residue is formed by all solids removed during the effluent treatment process. Conventional solutions of sending sludge to landfills or depositing it on land or in rivers are expensive and dangerous. This paper investigates the application of the stabilization/solidification technique for wastewater sludge using lime, cement and bitumen as additives. The modified soil samples were tested for the following parameters: California Bearing Ratio (CBR), Unconfined compressive strength (UCS), Indirect tensile strength (ITS), Resilient Modulus (RM), and deterioration tests (LWT e WTAT). The addition of 1% emulsion as an additive to the mixture supplied the highest increments in strength. Furthermore, the addition of only 1% of lime or cement increases the values of the tests by about 200%. These results are acceptable values for pavement purposes, from the structural point of view.

Effect of Reinforcing the Base of Pavement with Steel Geogrid

The report carries the information about tests of crushed-stone and sand sub-base of pavement reinforced with steel geogrid. As a result we have deformation characteristics of the base of pavement, the effect of reinforcing and deformation regularities of reinforced crushed-stone-sandy structures. We have determined the reinforcing coefficients of steel geogrid.