Design criteria for controlled low strength materials
Abstract
Controlled Low Strength Materials (CLSM) is now available under Department of Transportation specifications. Although a widely used material, some of its properties are not clearly studied and developed. Most of its properties are studied from field experience with exclusive usage, hence it may not be suitable in other applications. This study explores the properties of CLSM to develop better mix design. They are important to design CLSM mixes with consistent mix designs, workable and more flowable mixes, optimum utilization of waste materials, controlled density and strength, and suitability to specific applications. Although most CLSM applications are designed not to resist freeze and thaw deterioration, some specific applications are susceptible to deterioration. There are two ways to improve durability of CLSM. They are: (a) provide more air bubbles, and (b) increase strength. Selection methods are based on the application. Two important properties of CLSM are settings and strength development at early age. These are important to mixing, placing, and transporting CLSM, and to construction procedures. When time is a major concern, settings and strength development are important so a structure or facility can resume operation several hours after placement. Based on settings in concrete, two stages are defined: (a) Stiffening-stage, and (b) Hardening-stage. Stiffening-stage indicates a beginning of cohesion while Hardening-stage indicates hardening which load can be sustained. Some advantages of using CLSM as back-fill are: self-leveling, self-consolidation or self-compacted, and low long term settlement. The CLSM should easily flow and fill voids, hence flowability is important. There are two ways to improve the flowability: (a) increasing water content, and (b) increasing fly ash content. However, increasing water content is not encouraged due to segregation of particles. CLSM can be designed to meet Resilient modulus values rather than strength. This would enable its use in locations around structures to match the adjacent soil or to act as a transition between the high modulus of a structure and the relatively low modulus value of the soil. In addition, suitability of CLSM as subgrade material is better evaluated using resilient modulus.
Degree
Ph.D.
Advisors
Scholer, Purdue University.
Subject Area
Civil engineering
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