Browsing by Author "Semugaza, Gustave"
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- ItemComparative shrinkage properties of pavement materials including recycled concrete aggregates with and without cement stabilisation(Stellenbosch : University of Stellenbosch, 2016-03) Semugaza, Gustave; Rudman, Chantal; Jenkins, Kim Jonathan; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: The construction of pavement base/subbase layers necessitates quality materials such as natural aggregates. The use of locally available materials offers numerous advantages, including the reduction in the need for quarrying and transporting, which reduces the cost of construction. Unfortunately, these local materials don’t always perform adequately for structural purposes, and require stabilisation. Cement is considered as a binder that can treat various types of materials and provide good results. Although cement stabilisation increases the material strength properties, cement-stabilised materials are prone to shrinkage, which is recognised as the major source of different forms of cracking, identified as the most severe distress for pavements with Cement stabilised layers (CSL). Owing to friction from the layer below, high tensile stresses are induced in CSL, and cracking results when these stresses exceed the tensile strength of the material. The use of low cement content has been considered as basic measures to mitigate shrinkage, but it is not necessarily the case for all materials. In addition, the use of polymer cement additives has been considered for reducing the shrinkage in pavement layers. The Super-Absorbent Polymers (SAP) can reduce the shrinkage due to their high capacity of retaining large quantity of water. Both these factors were investigated, with the addition of SAP to Hornfels. The shortage of natural materials and strict laws on opening new borrow pits and landfills have made the recycling of wastes one of the highest requirements in many countries. A number of countries adopted the use of recycled Construction and Demolition Waste (CDW) as unbound base/subbase materials for pavements construction. Recycled CDW include Recycled Concrete and Masonry (RCM) and Recycled Concrete Aggregates (RCA). However, most of previous research has only considered cement stabilisation for natural materials. The consideration of cement stabilisation for these materials, which present self-cementing properties due to their nature, is essential. To evaluate the effect of self-cementing properties on the material shrinkage potential, this research compared the shrinkage properties of three materials, which include G4 hornfels, Recycled Concrete Aggregates (RCA), and New Concrete (NC). The G4 hornfels material served as the base material, and the NC material helped to assess the degree of self-cementation in the RCA material. Considering the shrinkage properties of the three materials, the results revealed that the cracking potential of the RCA material was very low, so that it could be used in place of G4 hornfels for base/subbase layers construction. In addition, the results revealed that the latent hydration (due to self-cementation) decreased the pivot-point of optimum percentage cement in the mix, when compared to that of the normal G4 material. The RCA and NC materials tended to reach their maximum shrinkage values at 2.5% cement content. The evaluation of shrinkage crack-patterns due to shrinkage results indicated that all cement-stabilised materials (all three material types) are classified as materials inducing unacceptable crack-patterns (very severe cracks). For non-stabilised materials, only the NC material is classified as a material inducing unacceptable crack-patterns. The non-stabilised RCA material is classified as a material inducing medium crack-pattern (severe cracks), while the G4 hornfels material is classified as a material inducing acceptable crack-pattern (no cracks). Referring to these crack-patterns, the consideration of methods for mitigating shrinkage cracks is necessary, if these materials are used in pavement layers. Nonetheless, it is evident that specifically RCA, although it has latent self-cementing properties, will not be subject to the same potential for cracking as NC.