Cement kiln dust (CKD) is the by-product of cement manufacturing. It is collected using air pollution control devices (APCDs) also known as electrostatic precipitators in the form of flue dust to minimize environmental hazards. This study investigates the potential use of CKD as a filler material and its novel antistripping properties on recycled asphalt pavement (RAP). CKD's chemical properties, make it desirable for improving stripping resistance of asphalt in areas prone to high rainfall or moisture exposure, but its application in RAP remains a grey area to explore. Its dual role in improving both adhesion and mechanical properties of asphalt makes it particularly advantageous, in terms of sustainability, cost and resource efficiency. The rising production cost, environmental safety concerns, and the push towards sustainable consumption/production seek alternatives for traditional antistripping agents for asphalt production, thus, CKD. This study prepared dense-graded asphalt concrete with nominal maximum aggregate size (NMAS) of 14 mm with 1%, 3%, and 5% of CKD by weight of RAP according to Malaysian standard. A total of five (5) asphalt concrete (AC14) mixtures were produced with an optimal 3% CKD used in the modified mixtures at the optimum binder content (OBC). The antistripping properties of CKD in hot mix asphalt (HMA) were assessed through indirect tensile strength test (ITS), indirect tensile stiffness modulus (ITSM) and boiling tests on the asphalt mixtures. In addition to the physical, mechanical, chemical, and structural/morphological tests, the safe inclusion of CKD in terms of heavy metals was evaluated by applying toxicity characteristic leaching procedure (TCLP) test. The findings confirm that CKD meets ASTM C150 standards for type II and type IIA hydraulic cement for use as a filler in asphalt. The fatigue cracking resistance, antistripping resistance in terms of the tensile strength ratio (TSR) & indirect tensile stiffness modulus (ITSM) tests indicated that CKD modified RAP mixes performed better than the control (CNTRL), RAP only and CKD modified RAP mixes. It also compares favourably with CNTRL + CKD mixture. Ultimately, the boiling test results indicated that CKD blended RAP mix surpassed the minimum 80% TSR for moisture damage resistance.

Industrial wastes cause damage to the environment and pose a threat to public health. The utilization of industrial wastes is inevitable if a circular economy needs to be achieved. Cement kiln dust (CKD) is a potential engineering material that can be used in many civil engineering works. The volume change behavior of a CKD is reported here. One-dimensional swelling and compression tests were carried out on CKD specimens to derive the compressibility parameters and coefficient of permeability. A cyclic wet-freeze-thaw-dry test was carried out to study the volume change of the material upon exposure to various seasonal climatic processes under a low surcharge pressure. The experimental results show that CKD can exhibit swelling under light loads. The correlations between plasticity properties and compressibility parameters that are applicable to fine-grained soils were found to overestimate the parameters of the CKD. The magnitudes of frost heave and thaw settlement were found to be significant, with an uprising type of movement accompanied by strain accumulation when the material was taken through several wet-freeze-thaw-dry cycles.

In response to the environmental challenges posed by conventional expansive soil stabilization methods, this study investigates the low-carbon potential of industrial by-products-cement kiln dust (CKD) and calcium carbide slag (CCS)-as sustainable stabilizers. A comprehensive series of laboratory tests, including compaction tests, free swelling rate measurements, unconfined compressive strength (UCS) evaluations, and scanning electron microscopy (SEM) analyses, were conducted on expansive soil samples treated with varying dosages in both single and binary formulations. The results indicate that the binary system significantly outperforms individual stabilizers; for example, a formulation containing 10% CKD and 9% CCS achieved a maximum dry density of 1.64 g/cm3, reduced the free swelling rate to 22.7% at 28 days, and reached a UCS of 371.3 kPa. SEM analysis further revealed that the enhanced performance is due to the synergistic formation of hydration products-namely calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H)-which effectively fill interparticle voids and reinforce soil structure. These findings demonstrate that the dual mechanism, combining rapid early-stage hydration from CCS with sustained long-term strength development from CKD, offers a cost-effective and environmentally sustainable alternative to traditional stabilizers for expansive soils.

Weak soils pose significant challenges for civil engineering projects, particularly in cold regions. Stabilizing such soils with additives is a common practice to enhance their geotechnical properties. This research aimed to evaluate the durability of clayey soils stabilized by alkaline-activated kaolin at 10, 25, and 50 %, along with 10 % recycled cement kiln dust (CKD). The stabilization process involved curing the soils at different temperatures (40, 60, and 80 degrees C) for varying durations (1, 7, 14, and 28 days). The stabilized soils underwent 5, 10, and 20 freezethaw(F-T) cycles to evaluate their durability. The results indicated F-T cycling led to a reduction in the unconfined compressive strength (UCS) of unstabilized soils, with a more pronounced impact as the number of F-T cycles increased. However, this adverse effect was mitigated by additive stabilization. The improvement in UCS in stabilized soils was directly linked to the additive content, curing duration, and temperature. Both additives demonstrated superior resistance to F-T cycling, with CKD outperforming kaolin. Study findings provided guidelines for utilizing kaolin and CKD for earthwork applications in cold regions with economic and sustainability advantages.

Although soil stabilization with cement and lime is widely used to overcome the low shear strength of soft clay, which can cause severe damage to the infrastructures founded on such soils, such binders have severe impacts on the environment in terms of increasing emissions of carbon dioxide and the consumption of energy. Therefore, it is necessary to investigate soil improvement using sustainable materials such as byproducts or natural resources as alternatives to conventional binders-cement and lime. In this study, the combination of cement kiln dust as a byproduct and zeolite was used to produce an alkali-activated matrix. The results showed that the strength increased from 124 kPa for the untreated clay to 572 kPa for clay treated with 30% activated stabilizer agent (activated cement kiln dust). Moreover, incorporating zeolite as a partial replacement of the activated cement kiln dust increased the strength drastically to 960 and 2530 kPa for zeolite ratios of 0.1 and 0.6, respectively, which then decreased sharply to 1167 and 800 kPa with further increasing zeolite/pr to 0.8 and 1.0, respectively. The soil that was improved with the activated stabilizer agents was tested under footings subjected to eccentric loading. The results of large-scale loading tests showed clear improvements in terms of increasing the bearing capacity and decreasing the tilt of the footings. Also, a reduction occurred due to the eccentricity decreasing as a result of increasing the thickness of the treated soil layer beneath the footing.

A large quantity of cement kiln dust (CKD) is produced annually during the production of Portland cement. The majority of the produced CKD remains unused except in specific cases related to soil stabilization projects. The current research investigates the production of self-compacting concrete (SCC) mixtures, in which CKD is used as a substitute for cement in different weight proportions, 3 %, 6 %, 9 %, 12 %, and 15 %. The hardened mechanical properties of SCC, such as compressive strength, splitting tensile strength, and flexural strength, as well as the fresh state characteristics (i.e., slump flow diameter, T500, V-funnel, and L-box tests), were recorded and compared with the control mixture which was entirely cast using cement. Results revealed that with an increase in the CKD content beyond 6 %, the slump flow diameter of SCC mixtures significantly decreased. Also, the increase ratios in the V-Funnel flow time for self-compacting concrete mixtures, when replacing cement with CKD ratios of 3 %, 6 %, 9 %, 12 %, and 15 %, were 13.3 %, 30 %, 46 %, 58 %, and 66.7 % respectively, compared with the reference mixture. Additionally, the impact behavior of two-way SCC slabs cast using CKD ratios ranging from 3 to 15 % and internally strengthened using various patterns of recycled plastic mesh was investigated. Strengthening the SCC slabs using two layers of recycled plastic grids proved to be effective in preventing the projectile from penetrating the whole thickness of the SCC slabs, regardless of the CKD content.

This paper investigates the effect of subgrade soil stabilization on the performance and life extension of flexible pavements. Several variables affecting soil stabilization were considered, including subgrade soil type (CL or CH), additive type and content (3, 6, and 9% of hydrated lime, 5, 10, and 15% of class C fly ash (CFA), and 5, 10, and 15% of cement kiln dust (CKD)), three stabilization thicknesses (15, 30, and 45 cm), and four pavement sections with varying thicknesses. The effects of these variables were investigated using four different damage mechanisms, including the fatigue life of the asphalt concrete (AC) and stabilized subgrade layers, the crushing life of the stabilized subgrade soil, and the rutting life of the pavement, using a non-linear mechanistic-empirical methodology. The results suggest that the optimum percentage that maximizes the pavement life occurs at 3% of lime for subgrade soil type CL, 6% of lime for subgrade type CH, and 15% of CFA and CKD for both subgrade soil types. The maximum pavement life increase occurred in the with the lowest thickness and the highest stabilization thickness, which was 1890% for 3% of lime in the CL subgrade and 568% for 6% of lime in the CH subgrade. The maximum increase in the pavement life of subgrade stabilization with 15% of CFA was 2048% in a CL subgrade, and 397% in a CH subgrade, and life extension due to subgrade stabilization with 15% of CKD was 2323% in a CL subgrade and 797% in a CH subgrade.

Cement production in the world market is steadily increasing. In 2000, it was 1600 million tons, while as of 2013, the annual amount exceeded 4000 million tons. The burning of cement clinker is associated with the generation of waste. It is estimated that the amount of cement kiln dust (CKD), during combustion, reaches about 15-20%, which means 700 million tons per year. However, not all types of by-products are reusable due to high alkali, sulfate, and chloride contents, which can adversely affect the environment. One environmentally friendly solution may be to use CKD in the production of high-performance concrete (HPC), as a substitute for some of the cement. This paper presents a study of the short- and long-term physical and mechanical properties of HPC with 5%, 10%, 15%, and 20% CKD additives. The experiments determined density, water absorption, porosity, splitting tensile strength, compressive strength, modulus of elasticity, ultrasonic pulse velocity, and evaluated the microstructure of the concrete. The addition of CKD up to 10% caused an increase in the 28- and 730-day compressive strengths, while the values decreased slightly when CKD concentration increased to 20%. Splitting tensile strength decreased proportionally with 5-20% amounts of CKD regardless of HPC age. Porosity, absorbability, and ultrasonic pulse velocity decreased with increasing cement dust, while the bulk density increased for HPC with CKD. Microstructure analyses showed a decrease in the content of calcium silicate hydrate (C-S-H), acceleration of setting, and formation of wider microcracks with an increase in CKD. From the results, it was shown that a 15% percentage addition of CKD can effectively replace cement in the production of HPC and contribute to reducing the amount of by-product from the burning of cement clinker.