Estimating the Maximum Time Delay Allowed Between Mixing Lime and Foamed Bitumen in Stabilised Pavements.

Estimating the Maximum Time Delay Allowed Between Mixing Lime and Foamed Bitumen in Stabilised Pavements.

Elliott Martin (n8578699)BEB801Bachelor of Civil and Environmental Engineering

ContextAustralia consists of a large network of roads.Roads must be adaptable to varying environmental conditions.Increase in modulus throughout the pavement.The time from the incorporation of lime to the soil, to the completion of foamed bitumen stabilisation is currently limited by Transport and Main Roads to 4 hours (excluding multi tyre rolling) and 6.5 hours (including multi tyre rolling).Disparity between contractors and Transport and Main Roads on the actual working time incited this topic.

SignificanceStabilisation is required in problematic soilsStabilisation increases the fatigue resistance of soil and can reduce pavement thickness, material selection, increases the life span of the pavement and minimises fatigue failure modes, significantly reducing construction time and associated costs. Increasing allowable the working times will give construction crews more leniency and minimise the impact of unforeseeable anomalies including machine malfunction and environmental conditions.

Scope

Aims and ObjectivesConduct a detailed literature review;Conduct a laboratory procedure to test the Technical Specification MRTS07C produced by Transport and Main Roads;Analyse the findings with Transport and Main Roads Technical Specification TN150.

History of Foamed BitumenIn 1956, Professor Ladi H Csanyi developed the fundamental technology.In 1968, Mobile Oil Australia acquired the patent to Csanyis innovation. In 1997, Queensland Department of Transport and Main Roads began trialling foamed bitumen for pavements in Queensland.Several organisations and contractors have continued research.

Foamed Bitumen Properties and PerformanceFoamed bitumen is the injection of cold water (2.5%) and expansion additive (0.5%) into hot bitumen (97%)Elementary it contains (82-88%) Carbon, (8-11%) Hydrogen, (0-6%) Sulphur, (1%) Oxygen, (1%) Nitrogen and 2000ppm metals (Nickel, Vanadium, Mercury, Lead, Chromium, Arsenic and Selenium).

Failure MechanismsCracking occurs when tensile strains and stresses exceed the allowable breaking strength of the pavement.At high temperatures, relaxation increases flexibility and prevents cracking, while low temperatures are more prone to cracking.Pavement ageing also plays a vital role in the ability to resist fatigue and tensile stress. As a pavement ages, it begins to oxidise, increasing the stiffness and reducing the relaxation capability, making it more susceptible to cracking.Cracking occurs in several configurations including; longitudinal cracking, transverse cracking, reflective cracking and crocodile cracking all of which are induced by various mechanisms. The mechanisms that cause these cracking configurations are; thermal cracking, low-temperature cracking, thermal fatigue, surface cracking and fatigue cracking.

History of Lime StabilisationThe use of lime as an in-situ stabilising treatment of natural soils has been around for more than 5000 years.Compacted soil-lime mixtures were used to stabilise the Pyramids of Shensi in Tibet.Municipalities and State Road Authorities have incorporated lime in urban and rural areas to improve stiffness, reduce Plasticity Index, enhance volumetric stability and increase longevity.

Lime Properties and PerformanceLime is a calcium-containing inorganic material consisting of (90-95%) Calcium Hydroxide, (0.5-1%) Magnesium Hydroxide, (0.1-2.5%) Water, (