A laboratory study of high-performance cold mix asphalt mixtures reinforced with natural and synthetic fibres

This research aims to examine the impact of using natural and synthetic fibres as reinforcing materials, on the mechanical properties and water susceptibility of cold mix asphalt (CMA) including indirect tensile stiffness and resistance to rutting, cracking and moisture damage. Four different types of fibres were used: glass as a synthetic fibre, and hemp, jute and coir as natural fibres. Various samples of CMA, with and without fibres, were fabricated and tested. Traditional hot mix asphalt (HMA) was also used for comparison. The results indi cate a significant improvement in the indirect tensile stiffness modulus, for all fibre-reinforced CMA mixtures, over different curing times. The improved tensile behaviour represents a substantial contribution towards slowing crack propagation in bituminous mixtures, while scanning electron microscopy analysis confirmed the fibre shape and surface roughness characteristics. The improved performance of the reinforced mixtures with both natural and synthetic fibres, facilitated a substantially lower permanent deformation than traditional hot and cold mixtures at two different temperatures (45 °C and 60 °C). When using glass and hemp fibres as reinforcing materials, there was a significant improvement in CMA in terms of water sensitivity. Resistance to surface cracking was also improved when fibres were incorporated. Based on the test results, 0.35% fibre content by mass of dry aggregate and 14 mm fibre length are recommended to achieve the optimum performance output for indirect tensile stiffness. © 2018 Elsevier Lt

Predicting the rutting behaviour of natural fibre-reinforced cold mix asphalt using the finite element method

This paper describes the development of a three-dimensional (3-D), finite element model (FEM) of flexible pavements made with cold mix asphalt (CMA), which has itself been reinforced with two different natural fibres: jute and coir. A 3-D finite element model was employed to predict the viscoelastic response of flexible CMA pavements when subjected to multiple axle loads, different bituminous material properties, tire speeds and temperatures. The analysis was conducted by the finite element computer package ABAQUS/STANDARD. The pavements were subject to cyclic and static loading conditions to test for permanent deformation (rutting). The accuracy of the developed model was validated by comparing the predicted results with those measured in the lab. Reinforced and unreinforced CMA mixture models were simulated in this research. The results indicate that the CMA mixtures reinforced with natural fibres, are effective in mitigating permanent deformation (rutting). These reinforcing materials can extend the service life of flexible pavements. © 2018 Elsevier Lt

DEVELOPMENT OF NEW COLD BITUMEN EMULSION MIXTURES AND FINITE ELEMENT MODELLING OF PREDICTING PERMANENT DEFORMATION

The increase of road infrastructure around the world involving the traditional hot mix asphalt (HMA) technology and its effects on the environment and health means that serious attention needs to be paid to building more sustainable flexible pavements. Cold bitumen emulsion mixture (CBEM) as an increasingly attractive cold asphalt mixture is therefore becoming an important subject area for study. Despite the efforts applied during the last few decades to enhance and develop CBEM application, certain issues still exist that make it inferior to HMA, resulting in limiting or minimizing its use. However, the enhancement of CBEM for flexible pavements construction, rehabilitation and maintenance is increasingly gaining interest in both pavement engineering industrial and research sectors. Therefore, the main aim of this study is to gain a deep insight and understanding into the impact response of using natural and synthetic fibres as reinforcing materials, on the mechanical properties and water susceptibility of CBEM including indirect tensile stiffness and resistance to rutting, cracking and moisture damage. Four different types of fibres were used: glass as a synthetic fibre, and hemp, jute and coir as natural fibres. Various samples of CBEM, with and without fibres, were fabricated and tested. Traditional hot mix asphalt mixture was also used for comparison. By achieving this aim it is expected that the use of CBEM would increase, allowing such mixtures to be used as structural pavement materials with some confidence. In spite of the quality of an asphalt mix being one of the most important and significant factors that affect the performance of both hot and cold mix flexible pavements, and the high quality mixes are often cost effective as these mixes require less maintenance and increase the service life of the pavements, it is also cost efficient to replace the semi-experimental flexible pavement design methods with fast and powerful software that includes finite element analysis. Several finite element models (FEM) have been developed to simulate the behaviour of hot mix asphalt, but none exists for cold mix asphalt reinforced by natural and synthetic fibres. This study also describes the development of a three-dimensional (3-D), finite element model of flexible pavements made with CBEMs, which has itself been reinforced with natural and synthetic fibres. The 3-D finite element model was employed to predict the viscoelastic and viscoplastic responses of flexible pavements based on CBEM when subjected to different multiple axle loads, bituminous material properties, tyre speeds and temperatures. The pavements were subject to moving and static loading conditions to test for permanent deformation (rutting). The results indicate a significant improvement in the indirect tensile stiffness modulus, for all fibre-reinforced CBEMs, over different curing times. The improved tensile behaviour represents a substantial contribution towards slowing crack propagation in bituminous mixtures, while scanning electron microscopy analysis confirmed the fibre shape and surface roughness characteristics. The improved performance of the reinforced mixtures with both natural and synthetic fibres facilitated a substantially lower permanent deformation than traditional hot and cold mixtures at two different temperatures (45 °C and 60 °C). When using glass and hemp fibres as reinforcing materials, there was a significant improvement in CBEM in terms of water sensitivity. These reinforcing materials can extend the service life of flexible pavements. Finally, the results show that the finite element model can successfully predict rutting of flexible pavements under different temperatures and wheel loading conditions

A viscoplastic model for permanent deformation prediction of reinforced cold mix asphalt

A reliable viscoplastic model of natural and synthetic fibres reinforced cold bitumen emulsion mixture is developed and applied to characterize the rutting behaviour of asphalt pavement by using finite element analysis. It is indicated that the traffic load parameters such as temperature, static loading condition and vehicular speed not only affects the rutting depth, it accelerates the rutting rate, causing the pavement earlier enter into rutting failure with shortened service life. Several finite element models (FEM) have been developed to simulate the behaviour of hot mix asphalts (HMAs), but none exists for cold mix asphalt (CMA) reinforced by natural and synthetic fibres. This research presents the first three dimension (3-D), finite element model (FEM) to assess the viscoplastic behaviour of reinforced CMA mixtures. The model is also able to predict rutting (permanent deformation) of asphalt mixtures under different traffic and environmental loadings, traditional HMA used as a comparison. The enhancement of the performance of CMA mixtures against permanent deformation using finite element software (ABAQUS) was validated by comparing the models’ predictions with measurements from wheel-tracking tests at different temperatures (45 °C and 60 °C). A very good level of agreement was found between the rutting predicted by the model and the experimental test. The results show that the finite element model can successfully predict rutting of flexible pavements under different temperatures and wheel loading conditions. Finally, the natural and synthetic fibres reinforced CMA mixtures are much more effective at resisting permanent deformation damage than conventional cold and hot asphalt mixtures. © 2018 Elsevier Lt

Impact of New Method for Laying Separate Sewer System on Pavement Layers

The method of installing underground infrastructure has a significant influence on road resistance and performance under live loads such as traffic. This research presents a new method for laying separate sewer systems by using one trench to sit both sanitary pipe and storm pipe and considers the effects of this approach on the pavement strength. Experimental tests have been conducted in the laboratory using a trench 2.5x0.45x1 metre to install two pipes one over the other (sanitary pipe in the bottom and storm pipe on top). Two cases have tested, the first case using 5 cm surface layer of cold mix asphalt while the second is using soil. A series of loads were applied to test the behaviour of this new system and its effects on the pavement surface layer and the buried pipe. The comparison between the rut print of the live load on the soil layer and the pavement layer was conducted. Results demonstrated that using the cold mix asphalt is still insufficient to provide enough safety to protect buried pipe as a reason of needing to relatively long time to acquire high stiffness. Therefore, minimum cover depth to protect pipelines still required

Shear performance of beam-column joints subjected to high loading rates

High loading rates may produce in structural frames due to some actions, such as explosions or debris impact. The response of structural members to such abnormal loadings should be investigated to provide comprehensive knowledge of their capability to resist impulsive forces. The beam-column joint is considered one of the most important structural components that significantly control the robustness and integrity of a structural frame. Hence, in the current study, eight full-scale specimens of two types of beam-column joints were tested under dynamic impact load to study their response to high rate load. These two types of joints were fin-plate and single angle-cleat joints. The tests were carried out using a drop hammer to apply an impact load on the specimens from different heights with different preloading conditions. The single angle-cleat joints exhibited a better response to dynamic loads with different impact height and preloading conditions than fin-plate joints in terms of resistance and ductility. Bolt shear failure was the dominant failure mode of the two types of the joints selected

The Impact of Cement Kiln Dust and Cement on Cold Mix Asphalt Characteristics at Different Climate

Cold bitumen emulsion mixtures (CBEMs) are made up of the same materials that are used in hot mixes. However, asphalt emulsion and water are used in such mixes. To date, many countries are still not using these mixes as a structure layer. This can be attributed mainly to their low resistance to rainfall, long curing time and low early strength. The addition of cementitious filler to CBEMs as a clean paving material is a potential technique to achieve superior mechanical qualities. The aim of this research is to compare improved CBEMs that might be used as a wearing surface to hot mix asphalt (HMA). These improvements were carried out through the use of a combination of cement and limestone, or a combination of ordinary Portland cement (OPC) and cement kiln dust (CKD). CBEMs were prepared according to Egyptian and British gradations using different percentages of ordinary Portland cement (OPC), CKD, and limestone. This may offer a new cold bitumen emulsion mixture to be used as a structural pavement layer in such countries. The main tests performed for the assessment of the mixes in this research are indirect tensile stiffness modulus, fatigue resistance, and resistance to rutting at different temperatures (20◦ C, 45◦ C, and 60◦ C). The results show that adding OPC to CBEMs enhanced the results in terms of ITSM, rutting and fatigue resistance. However, significant improvements were made by binary filler made of CKD and OPC to the said mechanical properties in terms of both UK and Egyptian gradations. The ITSM values for both CBEMUK6 and CBEMEg6, which contain 80% OPC + 20% CKD, improved by around 8 and 9 times in comparison to CBEMUK1 and CBEMEg1, which contain 20% OPC + 80% L.S, respectively

The future of eco-friendly cold mix asphalt

Road pavements are pivotal to the infrastructure, transportation and ultimate efficiency of both the public and the economy. However, they are undeniably having detrimental effects on an already compromised environment. Consequently, a re-think about road pavement construction materials is of paramount importance. Cold mix asphalt (CMA) is a low carbon manufacturing approach to the production of flexible pavement material that has proved to be very promising, both economically and ecologically. This technology allows the manufacture of mixtures at ambient temperatures without heating huge amounts of aggregates and bitumen, this decreasing CO2 emissions and saving energy. In spite of these positive impacts, CMA has a high sensitivity to traffic and environmental stresses due to the existence of water within the mixture, this of major concern to the industry. This study aims to review types of CMA and the main developments involved in cold bitumen emulsion mixture (CBEM) technology that can be used without decreasing in-service performance. This review also aims to provide a practical guide for the manufacture of bitumen emulsion and the design procedure of CBEM for the road pavements industry. Finally, it can be suggested that CMA is a crucial technique for pavement construction, as it provides acceptable performance alongside energy-saving and ecological objectives