Making road base and foundation from secondary waste minerals and recycled aggregates

Abstract

As the world is becoming aware of climate change and, as environmental policies and public concerns over the manufacture of cement and the extraction of our natural resources intensify, there is an increasing pressure and desperate need to use alternative materials to replace cement and primary aggregates. Environmental concerns over our desires for using products that are manufactured from the continuous extraction of our natural resources has necessitated a growing use of secondary waste minerals. In this research, comprehensive laboratory experiments were carried out to investigate the suitability of raw industrial by¬products to be used as cementitious materials. The raw industrial by-products used in this research were: PG, V-B5G, RAF, QWD, BPD-C, BPD-H, MHT, SSD and GGBS. The by¬products were obtained within the United Kingdom and predominantly sourced locally to develop a hydraulically bound cementitious material for applications in road (base), foundation and sub-grade in pavement construction for full replacement of Portland Cement.

Initial, material assessments were carried out based on X-ray diffraction (X-RD) and X-ray fluorescence (X-RF). High pozzolanic and / or cementitious properties were two important factors that were focused on for suitability of the raw materials in the research study. A broad range of laboratory tests were carried out to identify mechanical stability of the by-product binders and performance determined in strength development by time in terms of durability. High pressure flow tests were performed to determine the permeability of the materials and frost susceptibility tests were conducted to determine the freeze / thaw resistance of the materials. Absorption tests were carried out to determine the sorptivity of water by sustainable concrete made of by-products as binders and fines / coarse aggregates from recycled concrete. A statistical mixture design programme – Minitab 18, was used for the Design of Experiment (DoE). The Extreme Vertices Design (EVD) method was used to set the boundaries of the components in each group for the designs. Due to the high levels of materials used in some of the components, the combination of binary and ternary mixes was produced in the mix design. The effects of the combination of two / three mixes in the designs were considered in the analysis and discussions.

Eleven combinations of ternary binders referred to as ‘Groups’ were designed. There were thirteen mixes in each group. The first set (Groups 1 to 4) focused on the effects of MHT, RAF, BPD-C and BPD-H on mixes containing PG and GGBS. The second set (Groups 5 to 8) focused on the effects of MHT, RAF, BPD-C and BPD-H on mixes containing V-B5G and SSD. The third set (Groups 9 and 9A) concentrated on the effects of PG and V-B5G on mixes containing QWD and GGBS. Group 2A was added to compare the mechanical performance of the two gypsums used in the research, using the same mix design in mixes containing RAF and GGBS. Their results were analysed, and the preferred groups optimised to obtain the best mix known as ‘Warwickshire Blend.’ Most of the groups used the same water content. Specimens in the phase one laboratory tests were evaluated on Compressive Strength at 7, 14, 28 and 90 days curing. Groups 2, 2A and 9 were identified as the three top groups. Long-term durability studies were carried out on selected mixes from the three top groups to determine the novel blend.

It was discovered that strength development on the hydraulic pastes was slow during the early stages of hydration for mixtures containing 40 – 60% GGBS. After 28 days and up to 90 days when the ultimate strength (i.e. 90 days age) of the hydraulic paste is achieved, strength increases with the presence of GGBS of up to 60%. Mixtures with the proportions of 20% PG (Plasterboard Gypsum), 20% RAF (Reclaimed Asphalt Filler) and 60% GGBS for Group 2; 10% V-B5G (Vitamin B5 Gypsum), 30% RAF and 60% GGBS for Group 2A; and 10% PG, 30% QWD (Quarry Waste Dust), and 60% GGBS for Group 9 attained the highest compressive strengths of 41MPa, 40MPa and 38MPa respectively at 90 days. Not only did these mixes performed exceptionally well on compressive strength, their results on durability tests satisfied relevant standard tests. One of the dominant factors that influenced the strength of the mixes in Groups 2, 2A and 9 was the presence of calcium sulfate hydrate -(CaSO42H2O) in the PG, calcium sulfate -CaSO4 (CaO + SO3) in the V-B5G materials, calcium silicate – CaSiO3 (CaO + SiO2) in the GGBS and the pozzolanic activity (SiO2 + Fe2O3 + Al2O3) in the RAF and QWD. The results suggest that all the eleven groups used in the research study, have mixes suitable for use as hydraulically bound concrete road construction materials. Mix 13 of Group 9 with the proportions of 10% PG, 30% QWD and 60% GGBS was identified as the ‘Warwickshire Blend.’ The contribution to knowledge for this research was the use of two waste gypsums (PG and V-B5G) and two quarry by-products (RAF and QWD) in combination with GGBS as full cement replacement in road (base) and foundation.

Date of Award	Jul 2020
Original language	English
Awarding Institution	Coventry University
Supervisor	Eshmaiel Ganjian (Supervisor) & Morteza Khorami (Supervisor)