Suksun Horpibulsuk

Soil Stabilization by Calcium Carbide Residue and Fly Ash

Calcium carbide residue (CCR) and fly ash (FA) are both waste products from acetylene gas factories and power plants, respectively. The mixture of CCR and FA produces a cementitious material because CCR contains a lot of Ca(OH)2, while FA is a pozzolanic material. This paper investigates the possibility of using this cementitious material (a mixture of CCR and FA) to improve the strength of problematic silty clay in northeast Thailand. The influential factors involved in this study are water content, binder content, CCR∶FA ratio, and curing time. The mechanism controlling the development of strength is also illustrated. Strength development is investigated using the unconfined compression test. A microstructural study using a scanning electron microscope and thermal gravity analysis is performed to understand the microstructural changes that accompany the influential factors. Both strength and microstructural investigations reveal that the input of CCR reduces specific gravity and soil plasticity; thus, t...

Modelling the cutoff behavior of underground structure in multi-aquifer-aquitard groundwater system

The quaternary deposit of Shanghai is composed of an alternated multi-aquifer-aquitard system (MAAS) consisting of a sequence of aquitards laid over aquifers one by one. In the MAAS, any drawdown of groundwater head in an aquifer may cause consolidation of the overburden aquitard. When underground structures penetrate those aquifers, groundwater seepage path changes and drawdown occurs at the side characterized by the lower hydraulic potential along the flow direction (hereafter refers as to the lower side). This drawdown may cause additional subsidence at the lower side and unbalanced load between the two sides of the underground structure. In order to evaluate the cutoff effect of an underground structure on groundwater seepage in a MAAS representative of the underground of the city of Shanghai, a numerical analysis based on a groundwater flow model has been carried out. The simulated results have shown that underground structures which cut off groundwater flow locally change both magnitude and direction of the flow velocity field. The induced changes in the groundwater field are highly sensitive to the penetration depth and width of the underground structure. Design recommendations for underground structures in aquifers belonging to a MAAS are also presented, which has not yet been considered in the engineering practice of Shanghai.

Strength development in blended cement admixed saline clay

Abstract Cement stabilization is extensively used to improve engineering properties of soft saline clays. The effect of salinity, which is modified by geological and climate changes, on the strength development in cement admixed saline clay is investigated in this paper. For a particular curing time and salt content, the strength development in saline clay admixed with cement is governed by the clay-water/cement ratio, w c / C . The strength increases with the decrease of w c / C . The increase in salt content for a particular water content decreases the inter-particle attraction of the clay and the cementation bond strength. Hence, for the same clay-water/cement ratio, the strength of the cement admixed saline clay decreases with increasing salt content. In order to increase strength, and improve the economic and environmental impact, fly ash (FA) and biomass ash (BA) can be used to substitute Portland cement. The influence of FA and BA on the strength development of cement admixed saline clay was investigated with unconfined compressive (UC) test and thermogravimetric (TG) analysis. FA and BA were dispersing materials, increasing the reactive surface of the cement grains, and hence strength increases as well. The clay-water/cement ratio hypothesis was used successfully to analyze and assess the strength development of blended cement admixed saline clay at various salt contents. An addition of 25% ash can replace up to 15.8% of cement.

Evaluation of the Strength Increase of Marine Clay under Staged Embankment Loading: A Case Study

This article presents a case history of the performance of a full-scale test embankment constructed on a marine soft clay deposit improved by prefabricated vertical drains (PVDs) in the east of China. For analyzing the subsoil behavior, a 2D FEM model is established, in which the PVD-improved effect is considered by a simplified method of equivalent vertical hydraulic conductivity. The calculated results can predict the settlement behavior well; however, the FEM gives an underestimate for the value of excess pore pressures and it predicts similar values for the dissipation rate of excess pore pressures. The measured undrained shear strength of subsoil, Cu, is compared with the predicted value based on Ladd’s empirical equation and the Modified Cam-Clay model (MCC). The shear strength predicted by Ladd’s equation agrees well with the measured value, whereas the MCC overestimates the ability to improve subsoil shear strength during consolidation. The undrained shear strength of subsoil, Cu, increased as the construction progressed, and the shear strength incremental ratio, ΔCu/Δp′, decreased slightly with the degree of consolidation, U.

Engineering Properties of Silty Clay Stabilized with Calcium Carbide Residue

Calcium carbide residue (CCR) is a waste product from acetylene gas factories, which is rich in calcium hydroxide (CaðOHÞ2). Because clayey soils contain high amount of natural pozzolanic materials (silica and alumina), CCR can be used as a soil stabilizer. This article presents the engineering properties of CCR-stabilized silty clay to ascertain its performance in pavement base and subbase appli- cations. The input of CCR, which reduces the plasticity index of the clay, increases the optimum water content (OWC) and decreases the maximum dry unit weight (γd;max) of the stabilized clay. The CCR fixation point, simply obtained from the index test, is proved as a practical indicator for determining the CCR content to obtain the required engineering properties at a particular molding water content. The state of water content controls the densification, chemical reaction, and water absorption capacity. The soaked engineering properties are thus de- pendent upon the state of water content. For a particular CCR content, the optimum water content is the most appropriate in terms of strength, swelling and collapse behaviors, and bearing capacity. The lower water content is not sufficient for the chemical reaction, while the higher water content yields a higher water/binder ratio. The water absorption is smallest for the CCR-stabilized samples compacted at the OWC. To conclude, the optimal mix proportion is the CCR fixation point at OWC. CCR stabilization is more effective than lime stabilization in terms of engineering, economic, and environmental viewpoints. DOI: 10.1061/(ASCE)MT.1943-5533.0000618.

Influence of Wet-Dry Cycles on Compressive Strength of Calcium Carbide Residue-Fly Ash Stabilized Clay

This article studies the durability of the calcium carbide residue (CCR) and fly ash (FA) stabilized silty clay against wetting and drying cycles to ascertain its performance in pavement applications. The durability test on the CCR-FA stabilized clay samples compacted on dry and wet sides of optimum was performed according to the ASTM. The mixture of CCR and FA can be used for soil stabilization instead of ordinary portland cement. The suitable ingredient of CCR, FA, and clay results in a moderately high strength and durability geomaterial. The durability against wetting and drying (w-d) cycles of the CCR stabilized clay is considered low according to the recommendations of the American Concrete Institute and the U.S. Army Corps of Engineers and is not accepted as a pavement material. The input FA at optimal content reacts with the excess CaðOHÞ2 from the CCR, and hence a significant improvement of the strength and durability. The optimal FA content is found at about 20%. The strength analysis shows that the durability is directly related to the unsoaked strength (prior to the w-d cycles). Consequently, a relationship between thew-d cycle strength and unsoaked strength is proposed. It is useful for quick determination of unsoaked strength during mix design to attain the target strength at the design service life. DOI: 10.1061/(ASCE)MT.1943-5533.0000853.

Recycled-glass blends in pavement base/subbase applications: laboratory and field evaluation

AbstractThis paper presents the findings of a field and laboratory evaluation on the use of recycled glass blends as unbound pavement base/subbase materials. The parent recycled aggregates studied in this research were fine recycled glass (FRG), recycled concrete aggregate (RCA), and waste rock (WR). The geotechnical performance of the recycled aggregate blends of particular interest in this research were FRG blended with RCA (FRG/RCA) and FRG blended with WR (FRG/WR) in pavement base applications. The geotechnical performance of a trial road pavement was assessed by means of initial laboratory tests and subsequently field tests. The initial laboratory experimental program included specialized geotechnical tests including repeated load triaxial and triaxial tests to characterize the recycled materials. The subsequent trial road pavement constructed comprised seven different sections of FRG blends in the pavement base varying from 10 to 30% recycled glass content as well as two control sections with RCA an...

Modified Ohio's Curves: A Rapid Estimation of Compaction Curves for Coarse- and Fine-Grained Soils

Compaction curves from 16 coarse- and 9 fine-grained soils, which cover all soil types classified by the Unified Soil Classification System are analyzed to develop the Modified Ohio’s curves. For all soils, the relationships between water content and degree of saturation on both the dry and the wet sides of optimum are represented by power functions. Their compaction curves under standard Proctor energy follow the Ohio’s curves. Optimum degree of saturation, ODS, of coarse-grained soils is lower than that of fine-grained soils. However, for a given soil, the ODS is practically the same for different compaction energies, E. Even though compaction characteristics (optimum water content, OWC, and maximum dry unit weight, γd max) are different for different soils, their relationship between normalized OWC/OWCst and E is practically the same, where OWCst is the OWC at standard Proctor energy. Based on this finding, the Modified Ohio’s curves are introduced under compaction energy levels of the half standard, half modified, and modified Proctor energies. The verification of the Modified Ohio’s curve is also illustrated in this paper. These curves are useful in rapid estimation of laboratory compaction curves from a single set data of dry unit weight and water content.

Stabilisation of marginal lateritic soil using high calcium fly ash-based geopolymer

Marginal soils are traditional stabilised with Portland Cement (PC) when used as a pavement material. The production of PC is however an energy-intensive process and emits a large amount of greenhouse gas into the atmosphere. Geopolymer is an environmentally friendly ‘green’ binder commonly used in building applications but rarely used in pavement applications. The application of geopolymer to marginal soil stabilisation is an innovative approach given the increasing scarcity of virgin quarry materials in many countries. This research investigates the effects of alkali activator and curing time on unconfined compressive strength (UCS) and microstructural characteristics of marginal lateritic soil (LS) stabilised with high calcium fly ash (FA)-based geopolymer, which is novel in the field of pavement geotechnics. The viability of using this stabilised material as a bound pavement material was also evaluated through laboratory evaluation tests. A liquid alkali activator was a mixture of sodium silicate (Na2SiO3) solution and sodium hydroxide (NaOH) solution at various Na2SiO3:NaOH ratios. The results showed that the UCS increased with the curing time and the 7-day UCS for all Na2SiO3:NaOH ratios tested meets the local national standard as pavement bound material for both light and heavy traffic roads. The maximum early strengths at 7 days of curing were found at Na2SiO3:NaOH of 90:10, where calcium silicate hydrate (C-S-H), cementitious products from high calcium FA and Na2SiO3, was found to play a significant role. The sodium alumino silicate hydrate (N-A-S-H) products, being time-dependent, however came into play after a longer duration. The maximum 90-day UCS was found at a Na2SiO3:NaOH ratio of 50:50. This study indicated that marginal LS could be stabilised by high calcium FA-based geopolymer and used as an environmentally friendly pavement material, which would furthermore decrease the need for high-carbon PC. The economical Na2SiO3:NaOH ratio for both light and heavy traffic pavement materials was suggested to be 50:50.

ELECTRO-OSMOTIC CONSOLIDATION OF SOFT BANGKOK CLAY USING COPPER AND CARBON ELECTRODES WITH PVD

Electro-osmotic consolidation of Bangkok clay using copper and carbon electrodes with prefabricated vertical drain was studied. A laboratory testing program was conducted on undisturbed and reconstituted samples in a small cylinder cell and a large consolidometer in order to assess the probable effectiveness of electro-osmotic treatment. The tests were performed under the voltage gradients of 60 and 120 V/m with a polarity reversal of every 24 h. The time to achieve 90% degree of consolidation induced by electro-osmosis ranges from 1.4 to 2.1 and 1.2 to 2.2 times faster than the normal consolidation using PVD only for undisturbed and reconstituted samples, respectively. The faster rate of consolidation and higher magnitude of settlement were achieved at a higher voltage gradient. Higher reduction of water content up to 9% and increase in shear strength up to 144% were obtained using electro-osmotic consolidation with PVD compared to using PVD only, especially when using the carbon electrode. The liquid limit, plastic limit, and plasticity index were increased due to increased salinity during electro-osmotic consolidation. With its total dissolved salts of 4050 ppm well below the 6000 ppm limit, the soft Bangkok clay is considered to be suitable for electro-osmotic consolidation.