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The essential paving properties of soil, sand and stones
Published in Maxwell Lay, John Metcalf, Kieran Sharp, Paving Our Ways, 2020
Maxwell Lay, Metcalf John, Sharp Kieran
The voids in an unbound pavement are reduced by compaction during construction and by subsequent traffic loads. This relationship between compaction, moisture content and density is a key predictor of the performance of unbound pavement layers but did not come into prominence until experience with the compaction of the walls of earthen dams in the 20th century. Specifically, in 1929 Ralph Proctor of the Los Angeles Bureau of Waterworks showed that there is a maximum density that can be achieved with a given moisture content and amount of compaction, and the test to determine these values is now known as the Proctor test. In particular, the optimum moisture content is important as at this moisture content, the soil attains its maximum density for a given amount of compactive effort. It will always be less than the moisture content at which the soil is saturated.
Experiences with Liners Using Natural Materials
Published in T. H. Christensen, R. Cossu, R. Stegmann, Landfilling of Waste: Barriers, 2020
The dependence of clay liner hydraulic conductivity on degree of compaction and moisture content has been well described by Mundell and Bailey (1985), Daniel (1987) and Madsen and Mitchell (1989) among others. The nature of this dependence is shown in Fig. 1. It is first of all specific to the clay mixture being tested and cannot be applied to other soils. As a consequence, an equivalent data set must be generated for each liner material being considered. Figure 1(b) shows the traditional increased density with compaction effort and also the nonlinear dependence of density on moisture content resulting in an optimum moisture content to produce maximum density. Other compaction efforts produce other optimum conditions. The Standard Proctor and the Modified AASHTO (American Association of State Highway and Transportation Officials) are two compaction efforts frequently used in design specifications.
Aggregates
Published in M. Rashad Islam, Civil Engineering Materials, 2020
Gradation has a solid effect on material performance. The optimum gradation is a complicated topic. The desired characteristics, loading, environmental, material, structural, and mix property inputs vary depending on the material (AC or PCC). This section presents some important guidelines applicable to common, dense-graded mixes. The optimum gradation produces the maximum density. This involves a particle arrangement in which smaller particles are inserted among the larger particles, reducing the void space between particles. This creates more particle-to-particle contact, increases stability and reduces water infiltration in AC. In PCC, this reduced void space reduces the amount of cement paste required. However, having some minimum amount of void space present is necessary to: Provide adequate volume for the binderPromote rapid drainage and resistance to frost action for base and subbases
Development of designs for RCC mixtures with waste material
Published in International Journal of Pavement Engineering, 2021
Alireza Ameli, Ebrahim Parvaresh Karan, Seyed Amir Hossein Hashemi
The most common criteria for RCC are dry density, flexural strength, compressive strength, and toughness. Dry density is one of the most important parameters in construction of pavement mixtures including RCC. In many cases, it is essential to achieve the maximum density to improve the fatigue performance of pavements, the rutting resistance, and to extend the service life. Flexural strength is considered to be a key value when it comes to the stability of the concrete against deformation. Compressive strength of concrete is probably the most important and useful property. It determines the behaviour or response of the pavement while it experiences a compressive traffic load. Last, the toughness of concrete pavements is a fundamental parameter for estimating the load-bearing capacity and resistance of cracked pavements against crack growth. The property is so important in the regions with heavy traffic under cold and glacial climates.
Liquefaction susceptibility of non-plastic silty sands using hypoplastic model simulations
Published in International Journal of Geotechnical Engineering, 2021
M Akhila, K RangaSwamy, N Sankar
The minimum densities of soil combinations were obtained after placing the soil into the California Bearing Ratio (CBR) mould in a steady manner with zero height of falling using a paper cone and repeating this procedure three times to get the average value. Both the relative density and Proctor compaction tests were performed to obtain the maximum density of soil mixtures. The maximum densities of soil combinations were obtained after placing the CBR mould filled with soil sample over the relative density apparatus and exciting under shallow vibration amplitudes. The procedure was repeated three times and the average value is reported for each soil combination. Limiting void ratios (emax and emin) were determined from the obtained values of specific gravity and densities using mathematical relations.
Optimum moisture content in roller-compacted concrete pavement
Published in International Journal of Pavement Engineering, 2020
Payam Shafigh, Mohammad Hashemi, Boo Hyun Nam, Suhana Koting
Two methods are usually used for the mix design of RCCP. The first method is based on the workability of concrete to achieve the required consistency by adjusting water-to-cement ratio (w/c) and sand-to-cement ratio (s/c) (ACI 325-101995, Mardani-Aghabaglou et al. 2013). The second method is the maximum density method in which a mix design is based on the maximum dry density of concrete (ACI 2113R2002, Khayat and Libre 2014). The basic concept in this method is to maximise the packing density of solid materials by adjusting the moisture content. The optimum moisture content is defined as the moisture content corresponding to the maximum density in a moisture content–density curve and is dependent on properties of the aggregates used and the content of cementitious material (ACI 325-101995). For most aggregates, optimum moisture content is found within the range from 5% to 8% (Harrington et al. 2010). Fresh RCCP is stiffer than normal zero-slump concretes. The consistency of RCCP should be sufficiently stiff to remain stable under vibratory rollers and also sufficiently wet to permit adequate mixing and distribution of cement paste without segregation (Hodgkinson 1988, Aguiar-Moya et al. 2016, Du Plessis et al. 2016). Thus the required consistency of RCCP is different from conventional concrete consistency (Hodgkinson 1988, Harrington et al. 2010).