A novel multi-scale numerical model for prediction of texture-related impacts on fuel consumption

It is estimated that to overcome rolling resistance (RR) a typical vehicle, on average, consumes 4152 MJ/119 L of fuel annually, depending not only on vehicle-related factors but also on pavement-related factors. A slight improvement in surface properties may thus decrease fuel consumption, bringing substantial long-term socioeconomic benefits per capita per country. This aligns with ever-tighter limits on CO2 in the European Union (95 g/km until 2021), fostering sustainable construction and exploitation of tires and pavements. This paper outlines a newly developed multiscale three-dimensional numerical methodology to quantify texture-dependent RR due to indentation of aggregates into viscoelastic tread compound. It consists of a microscale tread block single-aggregate model and a macroscale car tire finite element model, rolling in a steady-state mode over a rigid smooth surface. Microscale interaction rates are deduced from the macroscale model. Tread compound is simulated by application of a time-dependent, linear, viscoelastic model. The microscale simulations enabled quantification of RR induced by an arrangement of surface aggregates. The outlined texture-dependent RR estimates are based on contact force moment around the contact patch center. The computed contact force results show a significant peak of normal force due to viscoelastic and inertia effects at the onset of the tire–surface contact phase, followed by a gradually decreasing/relaxing stress region with a sudden release at the end of the interaction. The contact forces seem to be of a reasonable distribution and magnitude. The proposed approach allows prediction of RR losses due to compressive forces at the microscale. Macro-distortional RR (which is not the subject of this paper) would then have to be added to find the total tire-related RR

Improvement of the service life of sustainable self-compacting concrete SCC by integrating high dosage of cement replacement

Based on simple diffusion theory and a timedependent factor (α) for the chloride diffusion coefficient, chloride penetration through concrete was numerically modelled and the service life was predicted. This was done for two reference mixes (normal vibrated concrete, NVC and selfcompacting concrete, SCC) and three other types of sustainable SCC incorporating high levels of cement replacement. All the mixes have a design compressive strength of 50-60 MPa at 28 days with different types of binders. In this study, the non-steady state chloride diffusion coefficients (Dnss) and the surface chloride concentrations (CS), which are mainly used for the numerical modelling of the chloride penetration phenomena, were calculated according to the recommendations of Nordtest methods NT BUILD 443 with the aid of using a developed excel solver tool. The numerical results indicated that the NVC at the same design strength level of the reference SCC showed lower service life and higher depth of cover design. For the sustainable SCC, the results showed that the incorporation of relatively high partial replacement of fly ash (FA) Class F and the combined high partial replacement of FA with the silica fume (SF) has little effect on the penetration parameter (Kcr) relative to that of reference-SCC. However, the incorporating of limestone powder (LP) at the same cement replacement ratio as other admixtures increased the Kcr, reduced the service life and increased the depth of cover design even when compared to the NVC at the same strength level

Macro/micro-pore structure characteristics and the chloride penetration of self-compacting concrete incorporating different types of filler and mineral admixture

The relationship between the internal pore structure features at different scales and the local micro-characteristics of the interfacial transition zone (ITZ) to the non-steady state chloride migration coefficient (Dnssm) is investigated for one normal and three types of sustainable high performance self-compacting concrete mixes. The pore structure classification at different scales and the percolation degrees of the ITZ’s pores were determined using both vacuum-saturated and Mercury Intrusion Porosimetry (MIP) techniques. Further, the local micro-permeation features of the ITZ, such as thickness, porosity and the chemistry of its hydration products is examined using the SEM coupled with the EDX analysis on polished, carbon-coated, flat specimens. Chloride movement was achieved using a modified rapid migration test. It was deduced that the degree of percolation of the pores of the ITZ had a significant role in controlling the chloride penetration process. Further, it is proposed that the ITZ thickness might be, primarily, responsible in determining the chloride ions’ migration velocity especially when coarse and unreactive filler are used. At nano scale, it is also suggested that the critical pore diameter in the cement matrix is more significant than is the average pore diameter in controlling the chloride resistance in SCC

The use of additives to enhance properties of pre-formed foamed concrete

This paper describes an experimental study of an enhancement of pre-formed foamed concrete, 1300-1900 kg/m3, by utilising two types of additives, silica fume and fly ash, to partially replace Portland cement and fine sand. It focuses on consistency, mechanical and thermal properties as well as presenting a comparison with normal weight, lightweight and foamed concretes from the literature. In addition to conventional foamed concrete mixes (FC), foamed concrete mixes with high flowability and strength (FCa) were also manufactured in this study. The FC mixes had 28-day compressive strengths from 6 to 23 MPa and corresponding thermal conductivities in the dry state from 0.475 to 0.951 W/mK, whereas for the same density range, the FCa mixes gave 19-47 MPa and 0.498-0.962 W/mK, respectively. Compared to other studies on foamed concrete, the results from the mixes investigated in this study showed higher strengths (for a given density), higher tensile to compressive strength ratios and higher moduli of elasticity

Pore structure and permeation characteristics of foamed concrete

A study has been undertaken to investigate the pore structure characteristics, porosity and critical pore diameter of preformed foamed concrete with a density between 1300 and 1900 kg/m3, and its effect on the permeation characteristics, water absorption and permeability. Different measured and calculated methods were adopted to determine the above properties and a comparison between them was done. Porosity was measured by apparent, total vacuum saturation and mercury intrusion porosimetry (MIP) methods, while permeability was measured (by constant and falling head methods) and calculated (by the Katz and Thompson model). Total porosity and dry density are found to be clearly related. The critical pore diameter (from the MIP test) and the pore diameter size (>200nm) are found to be closely related to the permeability of foamed concrete

Damage propagation rate and mechanical properties of recycled steel fiber-reinforced and cement-bound granular materials used in pavement structure

Cement-bound granular mixtures (CBGMs) represent an attractive option to increase load-carrying capacity and sustainability in highway construction. However, reflection cracking of overlying pavement layers due to the low tensile strength of CBGMs represents an important obstacle limiting their use. This study is undertaken to investigate how incorporation, in CBGMs, of recycled steel fibers extracted from old tires, at different cement levels may affect their tensile properties related to pavement design. A combination of three levels of cement (3%, 5% and 7% by wt. of aggregate and fiber) and two reinforcement contents (0% and 0.5 by volume of aggregate) was investigated. To comprehensively quantify the benefits of fibers in the presence of variable cement contents, time-dependent fracture and damage propagation were examined quantitatively utilizing a combination of macro-surface cracks, fractal analysis and both image monitoring and processing techniques. The results indicated better tensile strength and toughness after cement and fiber inclusion. Furthermore, increasing the amount of cement accelerates the crack propagation and damage dispersion rate while these two parameters reduced significantly in the case of fiber-reinforced cemented aggregate. All benefits gained from fiber usage are more evident at higher cement contents

Artificial SA-I and RA-I Afferents for Tactile Sensing of Ridges and Gratings

For robot touch to converge with the human sense of touch, artificial transduction should involve biologically-plausible population codes analogous to those of natural afferents. Using a biomimetic tactile sensor with 3d-printed skin based on the dermal-epidermal boundary, we propose two novel feature sets to mimic slowly-adapting and rapidly-adapting type-I tactile mechanoreceptor function. Their plausibility is tested with three classic experiments from the study of natural touch: impingement on a flat plate to probe adaptation and spatial modulation; stimulation by spatially-complex ridged stimuli to probe single afferent responses; and perception of grating orientation to probe the population response. Our results show a match between artificial and natural afferent responses in their sensitivity to edges and gaps; likewise, the human and robot psychometric functions match for grating orientation. These findings could benefit robot manipulation, prosthetics and the neurophysiology of touch

Suitability of mortars produced using laterite and ceramic wastes: mechanical and microscale analysis

Using industrial wastes and local materials as artificial aggregates in cement based materials remains a relevant measure for conservation of natural sources. In this study, novel cementitious mixes containing pulverized ceramic blended cement, ceramic aggregate and laterite were systematically combined to produce cement mortars. The mortar specimens were cured in water for a maximum of 28 days. At maturity, nondestructive tests, X-ray CT scan and ultrasonic pulse velocity, were performed on hardened mortars. Thereafter, a series of predefined properties, namely dry bulk density, compressive and flexural strength, water absorption coefficient (due to capillary) of the hardened mortars were determined. Finally, in order to understand the hydration mechanism of the materials as it relates to the strength properties, microscale tests, SEM and XRD, were used to examine the fragments of the selected mortars. From the results, a mortar sample containing 10% ceramic powder and 100% ceramic aggregate as replacements for cement and sand respectively, gave higher strength values than the reference and other mixes. Microstructural analysis of the best mix revealed that it has larger proportions of ettringite, portlandite and calcite than the reference mix, and this could be responsible for the strength gained. Thus, despite the apparent low reactivity of crushed ceramic material, this can improve bonding in cement-based mixture, when used at an appropriate concentration

Effect of cementation level on performance of rubberized cement-stabilized aggregate mixtures

An investigation and comparison is made of the effect of cement content on the performance of rubberized cement-stabilized aggregate mixtures and on cement-stabilized aggregate mixtures containing no rubber (RCSAMs and CSAMs). These materials are intended to be used as a base course for pavement structures. Three cement contents (3%, 5%, and 7% by dry weight of aggregate) were investigated. Rubberized mixtures were manufactured by replacing 30% of one aggregate fraction that has a similar gradation of crumb rubber. Performance was evaluated under static and dynamic testing. The investigated properties are unconfined compressive strength, indirect tensile strength, indirect tensile static modulus, toughness, dynamic modulus of elasticity, dynamic modulus of rigidity and dynamic Poisson's ratio. Increasing cement content increases strength of both types of mixtures, especially in the CSAMs. It is found that using crumb rubber at low cement content is more feasible than with high cement contents. Stiffnesses increased for both types of mixture as cement content increased but decreased on incorporation of crumb rubber. Energy absorption capacity was inversely related to stiffness. Mesostructural investigation revealed that the cracks were propagated through the rubber particles for all cement contents