Predictive Modeling and Optimization of Compressive Strength for Cold In-Place Recycling Base Course Incorporating Ground Coal Bottom Ash and Calcium Chloride

Pavement degradation throughout its design life requires rehabilitation to maintain its functionality. Conventional repair methods, such as ‘remove and replace,’ are costly and environmentally unfriendly. Cold in-place recycling (CIPR) has emerged as an eco-friendly alternative for addressing severe pavement damage. CIPR involves recycling the existing pavement and part of the base layer, which are then compacted to form a new base layer with the addition of a stabilizing agent. In Malaysia, cement is a commonly used stabilizing agent. However, the extensive use of cement raises environmental concerns, as its production contributes between 5-9% of global CO2 emissions. This study explores partially replacing ordinary Portland cement (OPC) with ground coal bottom ash (GCBA) and using calcium chloride (CaCl₂) as an accelerator to address this issue. The study varied OPC content from 1-4%, with GCBA and CaCl₂ ranging from 0-3%. An unconfined compressive strength (UCS) test was conducted to analyze the effects on compressive strength and strength development over time. Results indicated that the optimal GCBA percentage for cement replacement is 1%, while the optimal CaCl₂ content is between 1% and 2%. Overall, compressive strength increased with curing time, highlighting the potential of this innovative approach to pavement rehabilitation.

Flexible asphalt pavement relies on a strong road base layer for structural support throughout its service life. Deteriorated pavement conditions require continuous maintenance and rehabilitation, resulting in maintenance costs. Cold In-Place Recycling (CIPR) offers a sustainable and cost-effective solution compared to the conventional method of ‘remove and replace.’ CIPR involves recycling degraded existing pavement materials with a certain depth of aggregate base to form a new base layer, with the addition of stabilizing agents. Proper compaction before curing is crucial since inadequate compaction reduces base density, risking stability and causing rutting and deformation under traffic. This study investigated the compaction properties in CIPR-based pavement construction, integrating stabilizing agent comprising ordinary Portland cement (OPC), ground coal bottom ash (GCBA), and calcium chloride (CaCl₂) to achieve optimal moisture content (OMC), maximum dry density (MDD), and bulk density. Three different ratios of crushed aggregate (CA) and recycled asphalt pavement (RAP) were used, ranging from 25% to 75%, alongside 1% - 4% OPC, 0% - 3% GCBA, and 0% - 3% CaCl₂. It was discovered that the OMC and MDD values were 5.22% and 1.86 Mg/m³ for CA25RAP75, 5.60% and 1.93 Mg/m³ for CA50RAP50, and 5.87% and 1.94 Mg/m³ for CA75RAP25 using the modified Proctor test. Results also found that stabilizing agents minimally affect bulk density, but the percentages of CA and RAP significantly influence it, with design mixes with higher CA content providing higher bulk density. The findings from this study provide initial results on the OMC, MDD, and bulk density values but do not reliably indicate the strength acquired by the proposed design mix. Further strength tests should be considered.

The mechanical properties and heat development behavior of high strength concrete containing high fineness coal bottom ash as a pozzolanic binder

Utilization of industrial by-products as binders and fine aggregates for one-part lightweight controlled low-strength materials: Turning waste to value approach

Evaluation of compressive strength and resistance of chloride ingress of concrete using a novel binder from ground coal bottom ash and ground calcium carbide residue

The use of asphalt waste dust for stabilization of sustainable pavement recycling

Concrete construction offers a great opportunity to replace the cement with a coal-based power plant waste—known as coal bottom ash (CBA)—which offers great environmental and technical benefits. These are significant in sustainable concrete construction. This study aims to recycle CBA in concrete and evaluate its particle fineness influence on workability, compressive and tensile strength of concrete. In this study, a total of 120 specimens were prepared, in which ground CBA with a different fineness was used as a partial cement replacement of 0% to 30% the weight of cement. It was noticed that workability was decreased due to an increased amount of ground CBA, because it absorbed more water in the concrete mix. The growth in the compressive and tensile strength of concrete with ground CBA was not significant at the early ages. At 28 days, a targeted compressive strength of 35 MPa was achieved with the 10% ground CBA. However, it required a longer time to achieve a 44.5 MPa strength of control mix. This shows that the pozzolanic reaction was not initiated up to 28 days. It was experimentally explored that 10% ground CBA—having particle fineness around 65% to 75% and passed through 63 µm sieve—could achieve the adequate compressive and tensile strength of concrete. This study confirmed that the particle fineness of cement replacement materials has a significant influence on strength performance of concrete.

In this study, steel slag (SS) and ground coal bottom ash (GCBA) were utilized to partially substitute for cement in manufacturing ternary blended cement mortar. The replacement ratios of both SS and GCBA ranged from 0% to 20%, and the total replacement ratio varied from 0 to 40%. Response-surface methodology (RSM) and an artificial neural network (ANN) were employed to establish models with which the effects of the various combined contents of SS and GCBA on the distribution of 28-day strength and 91-day strength could be identified. The results showed that the combination of SS and GCBA had a positive effect on strength at a low replacement ratio, while it had an adverse effect on strength at a high replacement ratio. At a late curing age, the pozzolanic reaction of GCBA contributes to the strength enhancement. A total of 15 out of 27 experimental data were used to establish the RSM and ANN models. Through analysis of variance (ANOVA), the models established by RSM were well-fitted with the experimental data. The ANN-trained models also exhibited a good fit with the experimental data, as indicated by an R2 of >0.99. The remaining 12 out of 27 experimental data were used for the validation of the developed models, and the performances of the RSM and ANN models in prediction were compared. In conclusion, the ANN showed a better performance in strength prediction.

Cement production requires considerable energy and natural resources, severely impacting the environment due to harmful gas emissions. Coal bottom ash (CBA) and coal boiler slag (CBS), byproducts of coal-fired powerplants having pozzolanic properties, can be mechanically ground and replace cement in concrete, which reduces waste in landfills, preserves natural resources, and reduces health hazards. This study was performed to determine the optimum cement replacement amount of ground CBA (GCBA) and ground CBS (GCBS) in concrete, which was 10% for GCBA and 5% for GCBS. GCBA-based concrete exhibited superior tensile strength, modulus of elasticity, and durability compared to the control. In the Rapid Chloride Penetration Test, 10% GCBA concrete resulted in 2026 coulombs at 56 days, compared to 3405 coulombs for the control, indicating more resistance to chloride penetration. Incorporating 2.5% nanoclay in GCBA-based concrete increased the optimum GCBA content by 5%, and the compressive strength of 15% GCBA concrete increased by 4 MPa. The mortar consisting of the finest GCBA(L1) having Blaine fineness of 3072 g/cm2 yielded the highest compressive strength (32.7 MPa). The study discovered that the compressive strength of GCBA and GCBS-based mortars increases with fineness, and meeting the recommended fineness limit in ASTM C618 enhances concrete or mortar properties.

In Malaysia, seven coal-fired power plants under Tenaga Nasional Malaysia continuously produce around 790 tons of solid residue namely coal bottom ash (CBA) per day. The aim of this research was to optimize concrete mix design containing CBA as cement replacement via statistical modelling, response surface methodology (RSM). The fineness, water cement ratio and percentage inclusion of ground coal bottom ash (GCBA) were analyzed followed by RSM resulted on compressive strength at 28 days. Coal bottom ash was ground to three different sizes; 45 μm, 75 μm and 100 μm, water cement ratio was set to three different value; 0.40, 0.45 and 0.50 and percentage of GCBA inclusion was set up to three different percentages; 5%, 10% and 15%. Results indicate that GCBA increase compressive strength at 28 days regardless of different values of each variables. It is found that with the increasing percentage of inclusion of GCBA with lower water cement ratio will lower the compressive strength due to its characteristic of water absorbance. In conclusion, with adequate water cement ratio, and optimum percentage of GCBA, complete hydration process will be achieved, and the development of compressive strength is significantly increase.

Coal bottom ash (CBA) is claimed to carry some pozzolanic qualities that can be stimulated by pre-treatment. This study investigates the feasibility of partially replacing ordinary Portland cement (OPC) with ground CBA to produce CBA-cement paste. A thorough experimental program was designed to explore the effect of the CBA source and particle size, liquid-to-binder ratio (l/b), and superplasticizer (SP) on the 28-day compressive strength of CBA-cement paste. The CBA source with a high SiO2/Al2O3 ratio (approximately 3.6) and CaO content (5.3%) yielded higher compressive strengths. Grinding breaks down the large raw CBA particles and enhances their reactivity with water and pozzolanic character. Specimens with 50% ground CBA attained a 28-day compressive strength of up to 51 MPa at l/b of 0.225. The low pozzolanic nature combined with the porous texture of CBA necessitates the incorporation of a superplasticizer to enhance workability at low l/b. A 28-day strength of 61 MPa was achieved at 30% cement replacement with 150 μm CBA at l/b of 0.25 using 1% SP. In view of this, partial replacement of cement with ground CBA has proven to be a viable and sustainable construction option.

Pavement rehabilitation where the material in the existing pavement is recycled in-situ with bitumen will sustain the environment with conservation of natural aggregates, reduction in noise, dust emission and traffic disruption. This study investigate the effects of a native South African granular material stabilized with cement and bitumen emulsion as a base layer in pavement construction. The material stabilized with cement-bitumen emulsion (2-3%) was subjected to Unconfined Compressive Strength (UCS) and Indirect Tensile Strength (ITS) tests for 1, 4, 7 and 28 days curing. The UCS and ITS requirement was evaluated with respect to a base layer for design traffic application of less than six million equivalent single axles. The results of UCS and ITS tests for the stabilized material showed improved strength and have the potential for use as a base course material for the design traffic. The result revealed that 2.5% cement and bitumen emulsion meets the minimum strength characteristics for the base layer. Relative to 2% cement and 2% bitumen emulsion, ITS obtained for 4 and 7 days of curing increased approximately by 24%, 41% and 24%, 53% respectively. Models for UCS in terms of ITS was developed for cement and bitumen emulsion which will make one test among the two sufficient to indicate the strength of cement and bitumen emulsion stabilized materials at the mix design level. Bitumen stabilization is a quick construction method, with lower cost than reconstruction and good for rehabilitation. Keywords— bitumen emulsion, cement, granular, indirect tensile strength unconfined compressive strength.

Siliceous coal bottom ash is a residue originated in thermo-electrical power stations as a result of the hard coal combustion. It is expected that some characteristics of the coal bottom ash would be similar to those of the coal fly ash formed together in the same boiler. Coal bottom ash has a larger size than coal fly ash. Then, the first one was ground to achieve a particle size similar to the cement size. Therefore, to assess the sulphate resistance of cement-based materials made of ground coal bottom ash, sixteen Portland cement mixes were prepared by combining a cement CEM I 42.5 N according to the European standard EN 197-1:2011, a ground coal bottom ash and a coal fly ash. Both ashes were formed in the same boiler. The expansion measurements are considered to be an adequate parameter to assess damage due to sulphate attack of continuously submerged specimens. This procedure is the basis of the American standard ASTM C-1012/C1012 to evaluate the resistance of Portland cement and other cementitious materials to sulphate attack wherein the expansion measurements are taken with a standardized length comparator along the time. In this research program, the extent of sulphate attack was quantified by the percentage expansion of slender bars submerged in 5% sodium sulphate solution according to the ASTM C-1012 standard. This standard specifies an expansion limit of 0.01% for ordinary Portland cements CEM I and 0.035% for blended cements after a period of one year of exposure. The Portland cement CEM I 42.5 N made without ashes exhibited the largest expansion at 330 days (0.09%); whereas a cement with 10% of coal ash, CEM II/A-V, the expansion was much lower (0.03%) for both types of ashes. The expansion decreases when the ash content increases. In this property, no difference was found between ground coal bottom ash and coal fly ash provided by the same thermo-electrical power station.

Coal bottom ash is produced in electrical power stations as result of the coal combustion. Because coal fly ash and coal bottom ash are formed together in the same boiler, similar chemical and mineralogical composition is expected. The size and shape of these ashes is very different, and then, its effect on the performance must be studied. In order to get a similar grain size to that of the coal fly ash, the coal bottom ash was ground. Cement-based products are the main construction materials which manufacture requires the use of significant natural raw materials and energy. These manufacturing processes result in several types of emissions. In particular, the cement industry is under pressure to reduce CO2 emissions and some studies have shown different measures to reach CO2 reduction. For instance, reducing the clinker/cement factor will lead to a clear CO2 emission reduction. In this work, ground coal bottom ash is investigated to know its viability of being used as a new Portland cement constituent. Then, it is studied from a mechanical and durability point of view to evaluate the potential use of the coal bottom ash as an innovative binder. Ground coal bottom ash and fly ash mortars were more carbonated and exhibited a lower compressive strength than the reference mortars, but similar to each other. Keywords: coal bottom ash, Portland cement, Compressive strength, Durability

The viability of ground coal bottom ash as a potential Portland cement constituent to be used in building materials is assessed. Currently, coal fly ash is used to produce Portland cements and concretes. However, coal bottom ash is mainly landfilled. Gamma spectrometry analysis, compressive strength, physical and chemical testing were performed. The ground coal bottom ash activity concentration index (I = 1.03) was compared to that of the coal fly ash (I = 1.11) provided from the same thermo-electrical power plant. Ground coal bottom ash could be used in building materials in the same way as coal fly ash as a Portland cement constituent.