Emulsified asphalt mixtures have environmental, economical, and logistical advantages over hot mixtures. However, they have attracted little attention as structural layers due to their inadequate performance and susceptibility to early life damage by rainfall. The objective of this article is to provide an improved insight into how the mechanical properties of emulsion mixtures may be improved and to determine the influence of cement on emulsified asphalt mixtures. Laboratory tests on strength, temperature susceptibility, water damage, creep and permanent deformation were implemented to evaluate the mechanical properties of emulsified asphalt mixtures. The test results showed that mechanical properties of emulsified asphalt mixtures have significantly improved with Portland cement addition. This experimental study suggested that cement modified asphalt emulsion mixtures might be an alternate way of a structural layer material in pavement.

Effect of Cement on Emulsified Asphalt Mixtures

Review of the uses and modeling of bitumen from ancient to modern times

The performance of multilayered pavement systems depends strongly on interlayer bonding. To guarantee good bonding, tack coats (also called bond coats) are usually applied at various interfaces during pavement construction or overlay. The effectiveness of the tack coat can be assessed with the use of several devices arranged by different laboratories to evaluate interlayer shear resistance. This paper shows how interlayer shear resistance may be evaluated through the Ancona shear testing research and analysis (ASTRA) device. ASTRA results, expressed in units of maximum interlayer shear stress (τpeak) highlight the effects of various influence parameters such as type of interface treatment, curing time, procedure of specimen preparation, temperature, and applied normal load. Moreover, this paper compares the τpeak results obtained by two different shear test devices: the ASTRA tester designed and developed in the Polytechnic University of Marche (Italy) and the layer-parallel direct shear tester created by...

Advanced Testing and Characterization of Interlayer Shear Resistance

Earlier studies have demonstrated the beneficial effects of adding Ordinary Portland Cement (OPC) to bitumen emulsion mixtures. These effects were confirmed for some dense graded mixtures based on recipes currently used for hot mix in the UK and being considered for use in cold mix. Laboratory tests included stiffness modulus, resistance to permanent deformation and resistance to fatigue cracking. In order to obtain a clearer understanding of the mechanisms causing the improvements in properties, some basic studies were carried out. These included measurement of the rate at which coalescence of bitumen droplets developed and adhered to the aggregate particles, since this is the initial mechanism by which mechanical properties of the mixture are developed. The study was then extended to obtain an understanding of the properties of emulsion blended with OPC, hydrated lime or limestone filler. This was done since it was thought that a contribution to 'binding' of the aggregate in mixtures came from the hydration of cement as well as from the coalesced bitumen. Dynamic Shear Rheometer tests were used on various blends demonstrating the stiffening effects of both OPC and hydrated lime and that filler had little influence. The emulsifying process was also shown to have no effect on the characteristics of the base bitumen. Electron microscopy was used to study the crystalline structures of fully cured mixtures with and without OPC addition. Expert interpretation considered that some of the characteristics of cement hydration effects were present in those mixtures incorporating OPC. The study concluded that the improvements to key properties of cold mix by the addition of OPC can be explained by a range of mechanisms, including improved rate of emulsion coalescence after compaction, cement hydration and enhancement of binder viscosity.

A study of cement modified bitumen emulsion mixtures

This report discusses the benefits of using hydrated lime in hot mix asphalt paving mixtures. Some of these benefits include: control of water sensitivity, use as an antistrip agent to inhibit water damage, stiffens asphalt binders when used as a mineral filler, improves resistance to crack propagation, decreases damage from oxidation, improves moisture durability and stability by changing the properties of clay fines.

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Th e Benefi ts of HYDRATED LIME IN HOT MIX ASPHALT

The Dynamic Cone Penetrometer (DCP) has become one of the most useful testing devices in pavement evaluation in Israel and other parts of the world. Consequently, a reliable true meaning and interpretation of the results are needed. Research work dedicated to studying the effects of vertical confinement on the DCP strength values of the granular pavement layers and subgrade is summarized. Specifically, four major effects were studied: vertical confinement of granular layers, vertical confinement of cohesive layers, vertical confinement of rigid structural layers, and the effect of vertical confinement of upper asphalt layers on the DCP strength values of the granular layers below them. Based on engineering analysis and experimental testing in the laboratory and in the field, the following conclusions were made. (a) No vertical confinement effect by rigid pavement structure, the upper granular layers, or the upper cohesive layers on the DCP strength values of lower cohesive subgrade layers was found. Any differences in the results between the confined and unconfined DCP values can be explained by the friction that developed in the rod during tilted penetration. (b) However, vertical confinement effects by upper asphalt layers on the DCP values of the granular pavement layers exist. Since this is the true effect of the pavement structure, any DCP measurement for pavement evaluation purposes should be performed through a narrow boring in the asphalt layers and not after removal of a wide strip of asphalt. Generally, these confinement effects decrease the DCP values, and thus increase the structural strength measured. These confinement and friction effects, which can be evaluated quantitatively, should be taken into consideration when using the DCP method to evaluate existing pavements.

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Effect of vertical confinement on dynamic cone penetrometer strength values in pavement and subgrade evaluations

This paper presents a non-destructive pavement evaluation method based on continuous measurement with depth of pavement layers and subgrade parameters, using a Dynamic Cone Penetrometer (DCP). The DCP pavement evaluation method was developed based on extensive laboratory and field correlation testing. In the laboratory, conventional and DCP tests were made on a wide range of undisturbed and compacted fine grained soil samples, with and without saturation. Compacted granular soils were tested in flexible models with variable controlled lateral pressures. Field tests were made on natural and compacted layers representing a wide range of potential pavement and subgrade materials. Pavement evaluation tests were also performed for pavement and material evaluation and for correlation with pavement condition. The correlative laboratory and field testing program resulted in a quantitative relationship between the CBR of the material and its DCP value. This relationship was highly correlated for a wide range of pavement and subgrade materials. Based on the above extensive laboratory and field testing and analysis, a model was developed for realistic flexible pavement evaluation procedure. This is based on the DCP test through the entire pavement structure and down to the subgrade layers. The model relates the measured strength of individual pavement and subgrade layers and their relative contribution to the entire bearing capacity of the pavement structure. The model finally resulted in an equivalent thickness of a designed conventional pavement. This equivalent thickness can be interpreted either to the residual pavement life, i.e., the number of coverages of existing load down to a given terminal serviceability, or to the required overlay thickness (or other pavement remedy) for obtaining the designed pavement life. The paper presents the basic DCP test, the results of the correlative laboratory and field testing program, the models for highways and airport pavement and subgrade evaluation and results of the current method of pavement and subgrade evaluation using the DCP and its related models.

Pavement and material evaluation by a dynamic cone penetrometer. sixth international conference, structural design of asphalt pavements, volume i, proceedings, university of michigan, july 13-17, 1987, ann arbor, michigan

Moving bottlenecks in highway traffic are defined as a situation in which a slow-moving vehicle, be it a truck hauling heavy equipment or an oversized vehicle, or a long convey, disrupts the continuous flow of the general traffic. The effect of moving bottlenecks on traffic flow is an important factor in the evaluation of network performance. This effect, though, cannot be assessed properly by existing transportation tools, especially when the bottleneck travels relatively long distances in the network. This paper develops a dynamic traffic assignment (DTA) model that can evaluate the effects of moving bottlenecks on network performance in terms of both travel times and traveling paths. The model assumes that the characteristics of the moving bottleneck, such as traveling path, physical dimensions, and desired speed, are predefined and, therefore, suitable for planned conveys. The DTA model is based on a mesoscopic simulation network-loading procedure with unique features that allow assessing the special dynamic characteristics of a moving bottleneck. By permitting traffic density and speed to vary along a link, the simulation can capture the queue caused by the moving bottleneck while preserving the causality principles of traffic dynamics.

A dynamic traffic assignment model for the assessment of moving bottlenecks

Traditionally, asphalt rubber (AR) mixtures have been difficult to produce. Their production requires specialized plants and equipment, which has resulted in their high cost to manufacture. In part this difficulty is due to the need to produce AR binder by blending it at high temperatures for a significant period of time (typically at about 190°C for 45 min to 1 h). The complexities in the process have caused AR mixes to be significantly more expensive to produce than conventional paving mixtures. A new technology that produces a reacted and activated rubber (RAR), which is an elastomeric asphalt extender, has been developed by hot blending and activation of a rubber granulate with a selected asphalt binder and activated mineral binder stabilizer. RAR achieves results comparable to those of other types of polymer modified binders (PMBs). However, a principal advantage of RAR is that it can be added easily to any hot-mix asphalt manufacturing facility with systems designed to feed particulate material into...

Reacted and Activated Rubber: Elastomeric Asphalt Extender

A summary of some of the findings obtained during a series of research projects aimed to select, define, and evaluate the significant aggregate and filler properties and relate them to the behavior of bituminous concrete is presented. A concept and test method suggested for an objective quantitative evaluation of the geometric irregularity of aggregate particles (shape, angularity, and surface texture combined) in a wide range of particle sizes are discussed. The aggregate parameters were found to be significantly correlated to the physical properties and mechanical behavior of the bituminous mixtures composed of the aggregates tested. Research work and findings related to a special evaluation of important physicochemical properties of the filler and their significant effect on the immediate properties and the long-term durability behavior of bituminous paving mixtures are summarized.

Ilan Ishai

Papers

Effect of vertical confinement on dynamic cone penetrometer strength values in pavement and subgrade evaluations

Pavement and material evaluation by a dynamic cone penetrometer. sixth international conference, structural design of asphalt pavements, volume i, proceedings, university of michigan, july 13-17, 1987, ann arbor, michigan

A dynamic traffic assignment model for the assessment of moving bottlenecks

Reacted and Activated Rubber: Elastomeric Asphalt Extender

Effects of some aggregate and filler characteristics on behavior and durability of asphalt paving mixtures