Durability against wetting-drying cycles of water treatment sludge-fly ash geopolymer and water treatment sludge-cement and silty clay-cement systems

The viability of using two waste materials, water treatment sludge (WTS) and fly ash (FA), for developing sustainable masonry units has been previously investigated in terms of strength but the important aspect of durability against wetting–drying (w–d) cycles has yet to be studied. A study on durability against w–d cycles, an important parameter for service life design of the sustainable masonry units, is investigated in this paper. The liquid alkaline activator (L) was a mixture of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH), and a high calcium fly ash (FA) was used as a precursor. The results of cyclic w–d test indicate that the WTS–FA geopolymer manufactured with an optimum ingredient (L:FA=1.6, Na2SiO3:NaOH=90∶10) and at an optimum heat condition of 85°C for 72 h can be used as durable bearing masonry units; i.e., the compressive strength is greater than 12 MPa after 12 w–d cycles. For this optimum ingredient, the w–d cycle strength, qu(w−d) at heat temperatures between 65 and 95°C and durations between 24 and 120 h was found to be mainly dependent upon the initial soaked (without w–d cycle) strength qu0, and the normalized strength qu(w−d)/qu0 versus number of w–d cycles relationship expresses as a logarithm function. This relationship facilitates a mix design to attain the required strength at a target service life, which is very useful for civil engineering practitioners and researchers alike. It is evident from this research that portland cement is not a suitable cementing agent to manufacture WTS masonry units because alum in WTS retards the cement hydration, unlike a geopolymer binder, which was proven to be suitable. Compared with a traditional clay–cement sample at the same initial soaked strength, the WTS–FA geopolymer sample exhibits higher durability. This indicates that the WTS–FA geopolymer masonry units have a longer service life than clay–cement masonry units, which is typically used in many countries. This research enables WTS traditionally destined for landfill to be used in a sustainable manner as an aggregate in geopolymer masonry units, which is significant from engineering, economical, and environmental perspectives

Strength development of recycled concrete aggregate stabilized with fly ash-rice husk ash based geopolymer as pavement base material

This research studies on the usage of fly ash (FA) and rice husk ash (RHA) based geopolymers for improving the compressive strength of recycled concrete aggregate (RCA) to be a lightweight stabilised pavement base material. A mixture of FA from coal-burning power plants and RHA from rice milling process was used as a precursor while the liquid alkaline activator (L) was a mixture of sodium hydroxide solution (NaOH) and sodium silicate solution (Na2SiO3). Various RHA/FA ratios between 100/0 and 0/100 and NaOH/Na2SiO3 ratios between 50/50 and 100/0 were used in this study. The FA-RHA-geopolymer stabilised RCA samples, at each NaOH/Na2SiO3 ratio were prepared at the optimum liquid alkaline activator content (OLC) for unconfined compressive strength (UCS) tests. The UCS tests were conducted after 7, 28 and 60 days of curing. The test results indicate that the UCS of FA-RHA-geopolymer stabilised RCA increases as the RHA/FA and NaOH/Na2SiO3 ratios decrease and the curing time increases. Based on the Department of Highways, Thailand, the 60/40 RHA/FA and 60/40 NaOH/Na2SiO3 mix proportions are recommended for both low and high traffic volume roads with a low unit weight of 21.1kN/m3. This research study confirms the potential of FA-RHA-geopolymer stabilised RCA as an alternative stabilised road base material

Laboratory investigation of cement-stabilized marginal lateritic soil by crushed slag–fly ash replacement for pavement applications

Road construction consumes vast quantities of high-quality quarry materials. Lateritic soil (LS) is commonly used as a natural resource for subbase and base materials in Thailand. This research aims to study the feasibility of using crushed slag (CS) and fly ash (FA) to improve the physical properties of marginal LS prior to cement (C) stabilization for pavement applications. The pozzolanic materials in CS and FA were found to react with Ca(OH)2 produced by hydration, which results in the formation of cementitious products over time. Geotechnical engineering laboratory tests were conducted to evaluate the possibility of using cement stabilized LS/CS/FA blends as pavement subbase/base materials. The durability of the blends against wetting and drying cycles were also studied. The unconfined compressive strength (UCS) development of the mixtures was examined by using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. CS was found to have a high potential for minimizing swelling, which controls the durability of the stabilized material. Based on the specification of the Department of Highways, Thailand, the 3% C samples were found to be suitable as a subbase material when blended with 30% CS replacement and as a base material when blended with CS and FA at LS:CS:FA=70:0:30 and 70:15:15. The CS replacement was found to prolong the service life of stabilized subbases/bases with up to 12 wetting-drying cycles. This research confirms the possibility of incorporating LS/CS/FA in road work applications, with significant environmental benefits

Sustainable Soil Bearing Capacity Improvement Using Natural Limited Life Geotextile Reinforcement—A Review

Geotextiles are commercially made from synthetic fibres and have been used to enhance bearing capacity and to reduce the settlement of weak soil foundations. Several efforts have been made to investigate the possibility of using bio-based geotextiles for addressing environmental issues. This paper attempts to review previous studies on the bearing capacity improvement of soils reinforced with bio-based geotextiles under a vertical static load. The bearing capacity of the unreinforced foundation was used as a reference to illustrate the role of bio-based geotextiles in bearing capacity improvement. The effects of first geotextile depth to footing width ratio (d/B), geotextile spacing to footing width ratio (S/B), geotextile length to footing width ratio (L/B) and the number of reinforcement layers (N) on the bearing capacity were reviewed and presented in this paper. The optimum d/B ratio, which resulted in the maximum ultimate bearing capacity, was found to be in the range of 0.25–0.4. The optimum S/B ratio was in the range of 0.12–0.5. The most suitable L/B ratio, which resulted in better soil performance against vertical pressure, was about 3. Besides, the optimum number of layers providing the maximum bearing capacity was about three This article is useful as a guideline for a practical design and future research on the application of the natural geotextiles to improve the short-term bearing capacity of weak soil foundations in various sustainable geotechnical applications