The combined effects of the chemical stabilization of sediments using lime, cement and fly ash on the sediment shear strength behavior are studied for geotechnical purposes. An elemental analysis is carried out to examine the chemical aspects of stabilized sediments resulting from a series of chemical reactions. Direct shear strength measurements are performed to investigate shear strength improvements and stress-strain behavior of mix samples. A statistical analysis using the principal component analysis and the ANOVA (ANalysis Of Variance) method is also conducted to examine the correlation between cohesion and elemental ratio resulting from the chemical reactions. The analysis of the principal components suggests that Ca and Si and Al and K have greater impact on cohesion than the other elements. However, the ANOVA method reveals that the elemental ratios of Si, Al and Ca produce less impact on the sediment overall gain in cohesion at 28 days of curing. These results demonstrate that the gain in cohesion mostly depends on some other physical parameters, which need to be yet examined. The prediction equation of the cohesion indicates each elemental component gain weight on the overall cohesion gain resulting from the chemical reactions. In short, the considered equation still needs to be refined, notably in terms of performing further laboratory testing.

Contribution of fly ash (FA) as a complementary additive for dredged sediment (DS) stabilization was studied. The study is focused on definition of an efficient combination(s) to raise the DS properties. FA with lime and cement with both was used. Then, micro and macroscale investigations was performed. Test results demonstrate that FA additions promoted nucleation, formation of cementitious compounds and fabric modifications in sediment. DS stabilized using FA component show lower shrinkage and higher mechanical resistance than that stabilized using conventional binders. FA is found to be efficient in sediment-lime and sediment-cement mixtures since it accelerates cementation and strength gain.

Considerations on adhesion and moisture susceptibility of asphalt mixtures by mean of mechanical properties. 120p. Ph.D. Thesis

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Assim, na busca do uso benéfico deste resíduo, este trabalho tem como objetivo avaliar misturas de areia de fundição com solos argilosos, com a eventual adição de cal como agente estabilizante, à luz de algumas propriedades mecânicas da engenharia de pavimentos, visando o uso dos materiais resultantes na construção de estradas.

Abstract:Chemical stabilization is one of techniques which can improve mechanical and hydraulic properties of dredged sediments. This paper presents an experimental study focused on different techniques of stabilization of dredged sediment from La Baule-Le Pouliguen (France). Dredged sediments are stabilized with lime, Portland cement and fly ash. Three mixes were produced and submitted to uniaxial compression strength (UCS), indirect tensile strength (ITS) and shear tests at different curing ages. In addition, suction and mercury porosimetry tests are performed to highlight the effect of binders on the microstructure of treated sediment. Results indicated sediment treated with lime plus cement and fly ash, is promising, despite the time necessary to obtain the threshold of UCS (1MPa); unfortunately, ITS reference value (0.25 MPa) was not obtained. But this mixture presented good performance of shear strength parameters, exhibiting higher increases in cohesion (c) and friction angle () compared to the others mixes. In terms of porosimetry and suction results, it was observed that each type of binder acts differently, changing initial unimodal to bimodal porous distribution curves, and reducing suction in treated sediment due to macroporous occurrence and water retention for chemical reaction.

Cement stabilization improves physical and mechanical properties of geotechnical materials. However, numerous combinations of geotechnical materials and cement hinder to establish a pattern of mechanical behavior of cement-stabilized materials. Thus, this study aims to evaluate the mechanical behavior of soil-aggregate-cement mixtures (SAC) using high early-strength cement (HE), to contribute to dosage aspects and to ascertain their recommendation as base and/or subbase layers in heavy and very heavy volume roads. For this, SAC mixtures composed of different proportions of soil and aggregate (20:80 and 30:70) with 3, 5 and 7% of cement were produced and cured at different times (0, 7 and 28 days). Mechanical properties were assessed in terms of unconfined compressive strength (UCS), indirect tensile strength (ITS) and resilient modulus by repeated load triaxial test ( ) and by dynamic indirect tensile test ( ). A cement dosage study compared compressive and tensile strengths with acting stresses computed by mechanistic analysis of hypothetical pavements. This same procedure was also used for verifying the possibility of anticipating construction phases and reducing the traffic opening time, in this case a SAC mixture using Portland composite cement (PCC) was also evaluated. Results indicated that SAC-20:80 presented better mechanical behavior than SAC-30:70. Also, the cement content that led to the best mechanical behavior was 5%. All SAC mixtures with 5% HE had higher strength than the acting stresses interval computed for hypothetical pavements. SAC mixtures reached, at 7 and 3 days of curing, respectively, 80% and 60% of 28-days strength, which is the control parameter of Sao Paulo-DOT instructions for SAC. Findings indicated that, due to their good mechanical behavior, SAC mixtures are viable alternatives as layers in heavy and very heavy traffic pavements. Additionally, SAC’s high strengths at earlier curing times have shown their potential to reduce construction time.