Formulation et évaluation des méthodes de mise en oeuvre et d'essai en laboratoire sur l'endommagement et le recouvrement mécanique des bases granulaires traitées au ciment

Abstract

Globally, the road network suffers from underfunding and its complex requirements have pushed the Cement Association of Canada (CAC) to put forward a cost-effective, sustainable, versatile and efficient technique that consists of treating with cement granular bases of paved and unpaved roads. However, cement-treated bases (CTB) experience shrinkage during curing, which results in cracking. Reflective cracking leads to durability and performance issues, which limits the CTB usage. However, a new counter-intuitive approach to this problem is to intentionally damage the material at a young age, in order to induce a uniform microcracking pattern (precracking) which allows shrinkage distribution over a multitude of cracks. Thus, a mechanical recovery can be anticipated, because of the reduced severity of the cracks. Since this discovery, some projects have been interested by this method, but the results or implementation are poorly documented, incomplete or simply inaccessible. This current project aims to deepens the CTB precracking technique by developing in the laboratory a damage evaluation method, to understand its influence on mechanical properties. The formulation phase measured mechanical properties (compression, tension, CBR and modulus) and rheological properties (density, air content) over a combination between 3% and 5% of GU cement by granular mass (0–20 mm with sand), to which 5.2% water is added. Since there is no CTB standardization and very few test methods, a general evaluation of methods was essential. Thus, the different techniques of mixing, compaction and damage of CTB were studied, in addition to different methods of evaluation of hydration, shrinkage, cracking and microcracking. The various tests of the evaluation phase allowed a better understanding of the material and a judicious selection of the methods, both essential to begin the damage experimentation phase in the laboratory. The experimentation phase demonstrated the evolution of the mechanical properties (modulus, Poisson’s ratio, compressive strength) of undamaged CTB in time (1 day to 28 days). Also, the criteria and three levels of damage at 24 hours of cure were evaluated, in order to measure its influence on these same mechanical properties. Finally, the mechanical recovery was measured in the laboratory always by these same tests, up to 28 days after damage. The results showed that there is an optimal level of early-age damage for a full mechanical recovery at 28 days, that even surpasses the undamaged properties.

Date	7 Sept 2018
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Alan Carter (Supervisor) & Michel Vaillancourt (Co-supervisor)