This report presents information on the characterization of cementitiously stabilized layers and the properties that influence pavement performance. It also contains recommended performance-related procedures for characterizing these layers and performance-prediction models for incorporation into the mechanistic–empirical pavement analysis methods. Individual chapters highlight pavement distresses of hot-mix asphalt pavements and concrete pavements, laboratory tests and model development, and model calibration. The material contained in the report will be of immediate interest to state materials, pavement, and construction engineers and others involved in the different aspects of pavement design and construction.

Characterization of Cementitiously Stabilized Layers for Use in Pavement Design and Analysis

The effectiveness of fly ash use in the stabilization of organic soils and the factors that are likely to affect the degree of stabilization were studied. Unconfined compression and resilient modulus tests were conducted on organic soil–fly ash mixtures and untreated soil specimens. The unconfined compressive strength of organic soils can be increased using fly ash, but the amount of increase depends on the type of soil and characteristics of the fly ash. Resilient moduli of the slightly organic and organic soils can also be significantly improved. The increases in strength and stiffness are attributed primarily to cementing caused by pozzolanic reactions, although the reduction in water content resulting from the addition of dry fly ash solid also contributes to strength gain. The pozzolonic effect appears to diminish as the water content decreases. The significant characteristics of fly ash that affect the increase in unconfined compressive strength and resilient modulus include CaO content and CaO/SiO2...

Stabilization of Organic Soils with Fly Ash

Clayey soils in Syria cover a total area of more than 20,000 km 2 of the country, most of which are located in the southwestern region. In many places of the country, the clayey soils caused severe damage to infrastructures. Extensive studies have been carried out on the stabilization of clayey soils using lime. Syria is rich in both lime and natural pozzolana. However, few works have been conducted to investigate the influence of adding natural pozzolana on the geotechnical properties of lime-treated clayey soils. The aim of this paper is to understand the effect of adding natural pozzolana on some geotechnical properties of lime-stabilized clayey soils. Natural pozzolana and lime are added to soil within the range of 0%–20% and 0%–8%, respectively. Consistency, compaction, California bearing ratio (CBR) and linear shrinkage properties are particularly investigated. The test results show that the investigated properties of lime-treated clayey soils can be considerably enhanced when the natural pozzolana is added as a stabilizing agent. Analysis results of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) show significant changes in the microstructure of the treated clayey soil. A better flocculation of clayey particles and further formation of cementing materials in the natural pozzolana-lime-treated clayey soil are clearly observed.

Effect of adding natural pozzolana on geotechnical properties of lime-stabilized clayey soil

This paper presents the results of geotechnical and mineralogical investigations on lime treated clay soils from Hamedan City, Iran, and effects of pH variations on their shear strength parameters. Initially, lime was added in different percentages and laboratory experiments were conducted after curing times. The results indicate that these soils can be stabilized satisfactorily with the addition of about 7 % lime. Also, investigation of the relationship between lime-treated geotechnical properties and lime percentage and curing time demonstrates high regression coefficients for the proposed relationships. Several laboratory tests were performed on treated and untreated clay soils with lime mixed with pore fluids with different pH values including 3, 5, 7 and 9. The results of shear strength tests indicated that the undrained shear strength parameters for untreated clays increased considerably if the pore fluid had a high pH (pH = 9) or a low pH (pH = 3). It can also be found that for lime-treated soils, maximum cohesion and friction angle values are achieved at pH = 9.

Stabilization of clay soils using lime and effect of pH variations on shear strength parameters

Lime treatment is a well-known technique to improve the mechanical response of clayey subgrades of road pavements or clayey soils used for embankment. Several studies show that lime treatment significantly modifies the physical and hydromechanical properties of compacted soils. Nevertheless, studies on the scale effect under climatic changes are scarce. Actually, wetting–drying cycles might significantly modify the microstructure of treated soils, giving rise to changes in hydromechanical properties. This modification could be dependent on the size of soil aggregates before lime treatment. In the present work, this scale effect was studied by investigating the stiffness of a compacted lime-treated clayey soil using bender elements. The studied soil was first air-dried and ground into a target maximum soil aggregates size (Dmax). For each aggregate size, the soil was humidified to reach the target water contents wi, then mixed with 3% of lime powder (mass of lime divided by mass of dried soil) prior to the...

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Effects of the maximum soil aggregates size and cyclic wetting–drying on the stiffness of a lime-treated clayey soil

This paper presents the results of geotechnical and mineralogical investigations on lime-treated soft clay soil from Idku City, Egypt, where high organic matters of about 14% exist. Lime was added in the order of 1%, 3%, 5% and 7% by weight and laboratory experiments after 7, 15, 30 and 60 days were conducted including the mineralogical and microstructural examinations, grain size analysis, plasticity limits, unconfined compressive tests, vane shear tests and oedometer tests. The results indicate that soft clay soil of high organic content of 14% can be stabilized satisfactorily with the addition of 7% lime. The results also demonstrate that the changes in the mineralogical contents and soil fabric of high organic lime-treated soft clay improve soil plasticity, strength and compressibility.

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Utilization of Lime for Stabilizing Soft Clay Soil of High Organic Content

Model study of single pile with wings under uplift loads

Behavior of grouted single screw piles under inclined tensile loads in sand

Generally, foundations of many structures, such as transmission towers, bridge abutments, ocean engineering structures, marine dolphins, dock-fendering systems, and moorings are subjected to different modes of lateral loading. This research aims to study an alternative and novel technique to improve the lateral pile capacity in clay using fins at the top of piles. Laboratory small-scale model tests were carried out to study the behavior of laterally loaded finned piles installed in clay soil for different undrained shear strengths (Cu = 11 and 15 kPa). The effects of different factors, such as pile type, stiffness, geometric dimensions, and shapes of fins, were studied. Moreover, the effects of the fin number and inclination angle were also investigated. Results emphasized that there is an increase in the lateral pile resistance against the lateral load after placing fins at the top of the pile head. It has been found that the optimum length of the adopted fins should equal 0.4 of the pile embedded length and the fin width should equal the pile diameter. The existence of fins improved the behavior of finned piles by 1.67 and 1.55 for piles of L/D = 10 in the case ofCu = 11 and 15 kPa, respectively, compared to regular normal piles in the same condition. Also, the improvement in L/D = 22 piles due to fins reached to 1.29 and 1.35 for the case of Cu = 11 and 15 kPa, respectively.

Model study on the performance of single-finned piles in clay under lateral load

Strengthening of reinforced concrete (RC) beams with externally bonded fibre reinforced polymer (FRP) plates/sheets technique has become widespread in the last two decades. Although a great deal of research has been conducted on simply supported RC beams, a few studies have been carried out on continuous beams strengthened with FRP composites.  This paper presents a simple uniaxial nonlinear finite-element model (UNFEM) that is able to accurately estimate the load-carrying capacity and the behaviour of RC continuous beams flexurally strengthened with externally bonded FRP plates on both of the upper and lower fibres. A 21-degree of freedom element is proposed with layer-discretization of the cross-sections for finite element (FE) modelling. Realistic nonlinear constitutive relations are employed to describe the stress-strain behaviour of each component of the strengthened beam. The FE model is based on nonlinear fracture mechanics. The interfacial shear and normal stresses in the adhesive layer are presented using an analytical uncoupled cohesive zone model with a mixed-mode fracture criterion. The results of the proposed FE model are verified by comparison with various selected experimental measurements available in the literature. The numerical results of the plated beams (beams strengthened with FRP plates) agreed very well with the experimental results. The use of FRP increased the ultimate load capacity up to 100 % compared with the non-strengthened beams as occurred in series (S). The major objective of the current model is to help engineers’ model FRP-strengthened RC continuous beams in a simple manner.

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Mohamed A. Sakr

Papers

Utilization of Lime for Stabilizing Soft Clay Soil of High Organic Content

Model study of single pile with wings under uplift loads

Behavior of grouted single screw piles under inclined tensile loads in sand

Model study on the performance of single-finned piles in clay under lateral load

Analysis of RC Continuous Beams Strengthened with FRP Plates: A Finite Element Model