AbstractSignificant quantities of greenhouse gases have been emitted into the atmosphere from the processes of aggregate extraction and asphalt and Portland cement production in relation to the pavement construction industry. This issue can be tackled through the introduction of more sustainable construction materials made from industrial and construction wastes with low embodied carbon into infrastructure construction sector. As such, this research proposes innovative semi‐flexible composite pavement materials (SFC) comprising reclaimed asphalt planing aggregate skeletons infused with geopolymer cement‐based grouts. Both surface wearing and base courses were considered as potential applications for the proposed materials.
Geopolymer grout was formulated at ambient temperature using industrial by‐products such as fly ash, ground‐granulated blast‐furnace slag, metakaolin and silica fume to offer potential economic and environmental savings relative to ordinary Portland cement. By considering diverse binders with different physical properties and chemical compositions, a wide range of grout performance in terms of compressive strength and workability (i.e. flowability, initial and final setting time) was achieved to facilitate the manufacture of SFC suitable for a broad range of practical pavement applications. Mixture proportions and types of geopolymer powder were found to play critical roles in fresh and hardened
properties of geopolymer grout. As grout properties are fundamental to grouting processes and resultant SFC properties, four geopolymer grout types with contrasting performance classifications were investigated in detail to infuse open‐graded RAP skeletons for subsequent assessment of SFC properties.
A diverse suite of SFC mixtures was produced based on the four selected grout mixes and open‐graded RAP skeleton with various levels of solid contents, resulting in corresponding wide ranges of SFC properties such as permeable porosity, compressive strength and ultrasonic pulse velocity. Pronounced influences of grout properties and RAP content on SFC performance were found with increasing performance levels generally corresponded to highly flowable/high strength grout combined with decreasing RAP content. SFC materials with the ability to gain early strength with up to 84% of their 28‐day strength value after three days also offer promising benefits for pavements where early exposure to traffic is
mandatory. Comparable positive relationships enabling estimation of SFC elastic modulus based on rapidly attainable laboratory test methods such as ultrasonic pulse velocity and/or compressive strength are proposed to enable preliminary pavement designs incorporating layers made from SFC materials. The potential suitability of SFC materials for base layers has been successfully proven, with strength levels conforming to the
mechanical performance levels required by DMRB, volume 7, section 2, part 3 (Highways England, 2006a) for HBM base layers. The viability of SFCs as a replacement for traditional base layer materials were confirmed via preliminary pavement design examples. For instance, for heavy duty industrial hardstandings comprising 80 mm concrete block paving laid on a sand bed layer and subgrade CBR of 8%, base layer thickness requirements for SFC materials were lower than for conventional CBGM material.
In addition to mechanical and physical characterisation, costs of raw materials and greenhouse gas emissions to produce SFC base layers as an alternative to traditional CBGM base course in heavy duty pavements were carried out to evaluate its economic viability and environmental performance. SFC material costs and greenhouse gas emissions were lower than for traditional CBGM, highlighting their positive economic and environmental potential. By confirming a balance of technical, environmental and economic benefits associated with SFC, this reflects an excellent step towards a more sustainable future for pavement materials.
In addition to base course application, trafficking‐related properties associated with pavement wearing courses, such as specimen weight loss, skid resistance, mean texture depth and surface texture changes of surface courses, were also assessed for SFC materials using standard experimental and close‐range photogrammetry methods. Results from work to identifying suitable surface finishing methods for SFC showed that surface dressing is the most effective finishing method due to its high skid resistance values in dry and wet conditions. Based on this observation, further testing was carried out to determine its suitability for use in surface courses in pavements. SFC pavements with a surface dressing
finish comprising RAP and four geopolymer grout types were exposed to simulated trafficking conditions using Ulster University’s road test machine. Most of the investigated SFC specimens comprising average to high strength grout exhibited adequate endurance under traffic wear with low weight loss rate. As anticipated, SFC specimens comprising low strength grout showed significant weight loss associated with edge defects and cracks after a short length of time under polishing actions. Tested SFC specimens exceeded mean texture depth and skid resistance requirements for pavements made from conventional materials such as concrete or hot rolled asphalt with traffic of less than 2000 vehicle per
day (Department for Transport, 2010; Highways England, 2006b) but fell short of requirements for high friction surface.
Close‐range photogrammetry methods were found to provide valuable information on surface texture changes of SFC pavements during wearing process. Significant influences of simulated trafficking on SFC textures were highlighted based on notable changes in roughness, skewness and kurtosis parameters.
In general, the proposed SFC materials comprising geopolymer grout and recycled RAP as aggregates showed promising performance in terms of engineering properties as well as economic and environmental aspects to be used in pavement applications.
|Date of Award||Feb 2021|
|Supervisor||Bryan Magee (Supervisor) & David Woodward (Supervisor)|
- Semi-flexible composite
- Reclaimed asphalt pavement
- Compressive strength
- Skid resistance
- Close-range photogrammetry method