Title
Potential Utilization of Wheat Straw in Concrete for Pavement Applications from Engineering Perspectives
Abstract
The abundant availability of plant bres, around the globe, seeks researcher’s attention on their potential use as construction materials. There is a need to explore the structural integrity of concrete reinforced with such plant bres. To start with, among all plant bres, wheat straw is selected to be studied for its possible use as a construction material. As, out of 731 million tonnes global annual wheat production, Pakistan produces 26 million tonnes. Accordingly, 22 million tonnes wheat straw i.e. agricultural waste/by-product of wheat crop, is produced annually in Pakistan, depicting its abundant availability. On the other hand, the usage of rigid pavements has become more frequent over the past decades in developing countries. As per AASHTO pavement design guide, the serviceability of concrete pavements is almost 15% more than that of asphalt pavements for an averaged design life of 20 years. However, its more extensive use is still prevented due to its higher initial cost, mainly due to the cost of cement and reinforcement. Moreover, plain concrete is an inherently brittle material with low tensile strength and strain capacity. Accordingly, the pavement distresses, like early-age micro cracking and punch-outs etc., usually occur in rigid pavements, particularly in developing countries. These premature distresses can be minimized by using dispersed bres in concrete. Therefore, the overall aim of this research program is to have the development of economic and durable design and/or construction techniques for new rigid pavements by using locally available natural bres in concrete. However, natural bres reinforced concrete pavements are slightly explored yet. Furthermore, to the best of author’s knowledge, wheat straw is not studied yet for rigid pavement applications. Accordingly, the speci c aim of this doctoral study is to explore, in detail, the potential of wheat straw reinforced concrete for structural applications i.e. rigid pavements.
In this research program, in-depth investigation is made to evaluate the structural capacity of wheat straw reinforced concrete (WSRC) in terms of optimization, durability, and structural performance. The e ect of pre-treatment and content of wheat straw on the energy absorption capability of concrete has been studied by evaluating its static properties. Almost 25 mm long soaked, boiled, and chemically treated straw having content of 1%, 2%, and 3%, by mass of wet concrete, are considered. The durability of concrete having straw is determined, in terms of residual behaviors, after its exposure to room, climatic, and alternate wetting and drying conditions for 4-years. The contribution of wheat straw in improving the behavior and capacity of reinforced concrete for structural applications is also studied. WSRC beam-lets with varying texture and shear rebars are experimentally investigated. The structural performance of jointed WSRC pavement is also evaluated by constructing its test section. The laboratory and eld investigations are made to determine the compressive properties, detection measurements and cracks progression, after the exposure of test section to vehicular movement for 18-months. The properties of plain concrete (PC) specimens and test section are taken as reference. Micro-structural analysis is also done to verdict the straw behavior at all the stages.
Concrete, having soaked straw with 1% content, is optimized in terms of enhanced and durable properties. Splitting-tensile toughness index of concrete with 1% soaked straw is increased signi cantly by 105%. Optimized WSRC shows 79% residual textural strength under natural weathering. Structural and/or load carrying capacity of WSRC having textural and shear re-bars is enhanced up to 7.5%, along with the delayed crack initiation due to crack arresting mechanism provided by the presence of dispersed straw. WSRC pavement test section shows 34% higher energy absorption capacity, as compared to that of plain concrete section. Micro-structural analysis reveals that proper bonding between durable straw and concrete matrix is resulted is come out with enhanced properties. The structural performance of WSRC pavement (with 7% less design thickness as compared to PC pavement), in terms of load transfer eciency, is also enhanced up to 16%. Accordingly, the construction cost and carbon emissions of WSRC pavements can be reduced up to 14% and 28%, respectively. Hence, WSRC is recommended for economical and sustainable rigid pavements.