Sara Rios

Effect of the Porosity/Cement Ratio on the Compression of Cemented Soil

AbstractThe compression behavior of an artificially cemented soil was analyzed by the adjusted porosity/cement index using a correlation established in the recent literature. It was found that for each value of this index, defined as the ratio of porosity to the volumetric cement content, there was a unique normal compression line (NCL). The NCLs of the cemented specimens for each adjusted porosity/cement index did not converge with the NCL of the uncemented silty sand at large stresses, but reached a line parallel to it. The NCL of the cemented sand plotted further from the NCL of the uncemented sand as the porosity/cement index decreased.

Structural Performance of Alkali-Activated Soil Ash versus Soil Cement

AbstractAlkaline activation of fly ash (FA) was used to improve the mechanical performance of a silty sand, considering this new material as a replacement for soil-cement applications, namely, bases and subbases, for transportation infrastructures. For that purpose, specimens were molded from mixtures of soil, FA, and an alkaline activator made from sodium hydroxide and sodium silicate. Uniaxial compression tests showed that strength is highly increased by the addition of this new binder. The results described a high stiffness material, with an initial volume reduction followed by significant dilation. All specimens have clearly reached the respective yield surface during shearing, and peak-strength Mohr–Coulomb parameters were defined for each mixture. The evolution of the microstructure during curing, responsible for the mechanical behavior detected in the previous tests, was observed by scanning electron microscopy. These results were compared with soil-cement data obtained previously with the same soi...

Stiffness Behavior of Soil Stabilized with Alkali-Activated Fly Ash from Small to Large Strains

AbstractAlkaline activation of fly ash creates a geopolymeric cement that can replace ordinary portland cement in several applications such as soil improvement, with the advantage of much lower carbon dioxide emissions and reusing an industrial by-product otherwise landfilled, which averts several environmental problems. In this paper, the behavior of a silty sand improved by the alkaline activation of fly ash is analyzed from small to large strains by presenting uniaxial and drained triaxial compression test results and seismic wave velocities measured throughout the curing period. The dynamic, cyclic, and static tests showed a significant increase in stiffness with curing time, even beyond the 28-day curing period. On the basis of the nondestructive wave-propagation technique, the increase of the shear and compression wave velocities with time were drawn, giving the evolution of the elastic shear modulus and the Poisson ratio values. The dynamic Young modulus was compared to the correspondent secant You...

Mechanical and durability properties of a soil stabilised with an alkali-activated cement

Alkali-activated cements (AAC) have been extensively studied for different applications as an alternative to Portland cement (which has a high carbon footprint) and due to the possibility of including waste materials such fly ash or slags. However, few works have addressed the topic of stabilised soils with AAC for unpaved roads, with curing at ambient temperature, where the resistance to wetting and drying (WD) as well as the mechanical properties evolution over time is particularly relevant. In this paper, silty sand was stabilised with an AAC synthesised from low calcium fly ash and an alkaline solution made from sodium silicate and sodium hydroxide. The evolution of stiffness and strength up to 360 days, the tensile strength, and the performance during WD cycles were some of the characteristics analysed. Strength and stiffness results show a significant evolution far beyond the 28th curing day, but still with a reasonable short-term strength. Strength parameters deduced from triaxial tests were found to be very high with stress–strain behaviour typical of cemented soils. Durability properties related to resistance to immersion and WD cycles were found to comply with existing specifications for soil–cement, giving validity for its use as soil–cement replacement.

Increasing the reaction kinetics of alkali-activated fly ash binders for stabilisation of a silty sand pavement sub-base

The paper addresses several options to improve the reaction kinetics of alkali-activated low-calcium fly ash binders for soil stabilisation in road platforms. For that purpose, an experimental programme was established to assess the strength evolution, with time, of different binders, based on ash, lime, sodium chloride and alkali solutions, applied in the stabilisation of a silty sand. The tests included unconfined compression strength tests, triaxial tests and seismic wave measurements performed at different curing periods. The results were compared with a binder made of Portland cement and a commercial additive specifically designed for soil stabilisation in road applications. The activated ash mixtures with lime were the most performing producing a significant increase in the reactions development and, consequently, in the strength gain rate. The sodium chloride significantly improved the lime and lime-ash mixtures, but provided only a slight improvement in the activated ash mixtures.

Numerical Methodology to Minimize Resolution and Sensitivity Effects in P-Wave Measurements

This paper presents a new numerical methodology aiming at facilitating the identification of seismic wave’s propagation time, using a time domain approach. The solution uses first- and second-order differential computing, namely divided differences methods. Results of extensive laboratory seismic wave tests over aggregate–cement mixtures with different voids ratios (densities) and cement contents (1 %, 2 %, 3 %, 4 %, and 5 %) are discussed. The results indicated relevant differences in values of longitudinal modulus (or P-wave modulus) derived with and without this methodology. This was considered especially important in stiff specimens with high-seismic wave velocities and low-energy input signals.

Seepage water quality of a soil treated with alkali-activated cement at room temperature

Modern societies are great producers of waste because of their energy and natural resource needs. Many of these wastes are disposed of in landfills, which require a significantly sized area of soil...

Geotechnical Properties of Sediments by In Situ Tests

River sediments are mainly composed by intermediate materials, between sand and clay, for which partial drainage conditions apply. In these cases, the interpretation of CPTU tests may be wrong since existing correlations are based on fully drained or fully undrained conditions. This paper presents results from CPTU tests performed in a river area to evaluate whether partial drainage conditions were observed. The results, presented in terms of the normalized velocity, show that great part of the analyzed profiles are in this condition. For this reason, the angle of shearing resistance was presented as a conservative estimate of the soil strength in these areas.

Characterization of Soil Treated With Alkali-Activated Cement in Large-Scale Specimens

Soil improvement with hydraulic binders is currently used in practice because of the advantages of using the local soil enhancing its geotechnical properties. However, environmental issues related to quicklime applications and carbon-dioxide emissions associated to Portland cement production encouraged the development of new binders. In this work, alkaline-activated cement (AAC) synthetized by fly ash and an alkaline solution was used to stabilize silty sand. The behavior of the treated soil was evaluated performing tests on a physical model and the results were compared to laboratory data to define its compaction, strength, and stiffness properties. Those tests include nuclear density gauge measurements, light falling weight deflectometer tests, and plate load tests, whereas unconfined compression tests with unload–reload cycles and seismic wave measurements were performed at the laboratory. These tests, very common in current geotechnical practice, have proved to be also adequate to quality control and to evaluate the geomechanical properties of this material. The results at 28 days show a significant improvement given by the AAC, but still show some sensitivity to water when flooded. The comparison of results from different tests provided the evolution of stiffness with strain level.