Physical-Mechanical Performance of Concrete with Agro-Industrial Ashes at Different Thermal Curing Ranges

The construction industry faces the challenge of reducing its environmental impact, since cement, an essential component of concrete, is responsible for approximately 8% of global CO₂ emissions [1]. This situation has encouraged the search for supplementary materials capable of reducing clinker content without compromising the physical and mechanical performance of concrete. Among the alternatives explored are mineral additives, natural pozzolans, and agro-industrial by-products, whose use can enhance material performance while contributing to the principles of the circular economy [2-5].

In Peru, sugarcane and rice are widely cultivated crops, generating significant volumes of agro-industrial waste, particularly sugarcane bagasse ash (SCBA) and rice husk ash (RHA). Both by-products, after appropriate calcination and grinding processes, present a high content of reactive silica and other compounds with pozzolanic potential. These compounds are capable of reacting with the calcium hydroxide released during cement hydration, promoting microstructural densification and reducing porosity [5-9]. Their incorporation also contributes to lower cement consumption, improved waste management, and mitigation of the carbon footprint associated with construction activities [10-13].

Previous studies have reported increases in compressive and tensile strength, as well as improvements in cohesion and workability, when cement is partially replaced with SCBA or RHA at moderate proportions [12, 14-16]. In particular, replacement levels between 5% and 10% have been identified as optimal, achieving higher compressive strength compared to conventional concrete mixtures [12, 16-18]. However, most of these investigations have been conducted under standard curing conditions, without systematically assessing how the performance of SCBA- and RHA-modified concretes varies under different curing temperatures [19-22].

This limitation is especially relevant in the Peruvian context, where construction activities take place under marked thermal variability. In high Andean regions, ambient temperatures may fall below 10℃, whereas in coastal and jungle areas they can exceed 30℃ [13, 23-25]. Such temperature variations directly influence hydration kinetics: low temperatures delay early strength development, while elevated temperatures accelerate hydration but may induce microcracking and reduce long-term durability if not properly controlled [26-29].

Within this framework, the present study aims to evaluate the influence of partial cement replacement with SCBA and RHA, at proportions of 5% and 10%, on the physical and mechanical properties of concrete designed for f′c = 210 kg/cm² and subjected to controlled curing temperatures of 10℃, 25℃, and 35℃. Unlike previous studies, this research integrates a comparative analysis across three contrasting thermal ranges, considering both fresh-state and hardened-state properties and applying statistical validation methods (Analysis of Variance (ANOVA) and Tukey tests) to identify significant differences. The results are intended to support technical recommendations for the use of these additions under different climatic conditions in Peru, thereby promoting the production of more sustainable concrete aligned with Sustainable Development Goal No. 12: Responsible Production and Consumption.

Table 1 presents the chemical composition of the sugarcane bagasse ash (SCBA), expressed as mass percentage, based on data obtained from the X-ray fluorescence analysis report. The results indicate a combined content of 91.67% for silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), and iron oxide (Fe₂O₃), which complies with the requirements established in Annex A of NTP 334.014, where a minimum value of 70% is specified for these compounds. In addition, the sulfur trioxide (SO₃) content was 0.07%, remaining well below the maximum permissible limit of 4.00% established by the same standard. Regarding loss on ignition, a value of 4.20% was obtained, which also complies with the regulatory requirement of not exceeding 10.00% according to NTP 334.014.

Table 1. SCBA chemical composition proportion percentage comparison

Table 2 presents the granulometric analysis performed at the SCBA, to obtain a smaller particle size that passes through mesh No. 200, obtaining 84.9% with respect to the percentage in mass. All through, ash from the No. 200 mesh was used for the mixing design of the specimens.

Table 2. SCBA granulometry

Table 3 presents the composition of the RHA, expressed as a percentage by mass, according to data obtained in the X-Ray Fluorescence Analysis Report, the results show a record of 94.92% in the sum of silicon dioxide (SiO₂), aluminum oxide (Al₂O₃) and iron oxide (Fe₂O₃), complying with the provisions of Annex A of NTP 334.014, which requires a minimum of 70% of these compounds. Likewise, the content of sulfur trioxide (SO₃) is 0.02%, a value that is within the allowed limit compared to the norm of 4.00% at most.

Table 3. RHA chemical composition proportion percentage comparison

With respect to the loss due to burning, 1.60% was obtained, complying with the regulatory requirement of not exceeding 10.00% of the aforementioned standard.

Table 4 presents the granulometric analysis carried out at the RHA, whose objective was to obtain a smaller particle size that passes through the No. 200 mesh, obtaining 66.8% with respect to the percentage by mass. All through, ash from the No. 200 mesh was used for the mixing design of the specimens.

Table 4. RHA granulometry

The results obtained demonstrate that the incorporation of SCBA and RHA differentially modifies concrete properties as a function of curing temperature, confirming that their performance is strongly governed by hydration kinetics and the pozzolanic characteristics of each addition [16-18].

At medium and high curing temperatures (25–35℃), the observed increase in compressive strength of up to 14% for the mixture containing 5% SCBA+RHA can be attributed to the synergistic interaction between both ashes. Their high contents of amorphous silica (SiO₂) and alumina (Al₂O₃) react with the calcium hydroxide (Ca(OH)₂) released during cement hydration, leading to the formation of additional calcium silicate hydrate (C–S–H) and, to a lesser extent, calcium aluminate hydrates (C–A–H) [13, 19, 20]. This microstructural refinement reduces capillary porosity and increases matrix densification, which is consistent with previous findings reported for RHA [16, 19], SCBA [20], and other agro-industrial pozzolanic materials [21, 22].

In contrast, at a curing temperature of 10℃, pozzolanic reactions are significantly slowed due to reduced solubility of reactive compounds and limited ion diffusion within the pore solution, which restricts early C–S–H formation [23]. This behavior explains the limited improvements or even reductions observed in indirect tensile strength, such as the 17% decrease recorded for the mixture containing 10% RHA. Similar trends have been reported in previous studies [24, 25], which indicate that pozzolanic additions in cold climates require extended curing periods or thermal control to fully develop their reaction potential.

Regarding physical properties, the reduction in slump observed for mixtures with 10% replacement levels (up to −28% relative to the control) reflects decreased workability. This effect is mainly associated with the higher proportion of fine particles, increased specific surface area, and internal porosity of the ashes, which intensify initial water absorption [13]. However, these same characteristics contribute to a reduction in bleeding (up to −18%), thereby enhancing mixture cohesion and reducing the risk of segregation. Similar behavior has been reported for other fine mineral additions, such as fly ash and microsilica [26, 27].

A comparative analysis between SCBA and RHA indicates that RHA exhibits superior performance in indirect tensile strength at 35℃, with increases of up to 14%. This behavior can be associated with its high chemical purity and fineness, which promote the development of a more homogeneous and mechanically efficient interfacial transition zone (ITZ) between the cement paste and the aggregates [16, 26]. Conversely, SCBA showed more consistent improvements in compressive strength, possibly due to its higher content of aluminates and metal oxides, which favor the formation of secondary hydration products capable of resisting compressive loads, such as calcium aluminate hydrates [20, 28].

From a practical standpoint, these findings suggest that in coastal and jungle regions of Peru, where curing temperatures commonly exceed 20℃, the incorporation of SCBA and RHA—particularly in combined proportions of 5%—can simultaneously enhance mechanical performance and mixture cohesion, contributing to more durable and sustainable concrete. In high Andean regions, where curing temperatures may approach or fall below 10℃, extended curing durations or temperature-controlled curing regimes are recommended to prevent performance losses, especially in terms of tensile strength [24, 25].

Notably, the maximum strength gains observed in this study (up to 14% in compressive strength at 25–35℃) exceed the improvements typically reported in previous studies involving similar agro-industrial pozzolanic additions, which generally range from 8% to 12% under comparable curing conditions [16, 19, 21]. This enhanced performance suggests a pronounced synergistic effect resulting from the combined use of SCBA and RHA, likely due to the complementarity of their chemical composition and particle size distribution, which optimizes cementitious matrix densification.

Despite these findings, the study presents certain limitations, including the absence of microstructural characterization techniques, such as scanning electron microscopy (SEM) and X-ray diffraction (XRD), to directly confirm the morphology and composition of hydration products. Additionally, long-term durability aspects—such as carbonation resistance, sulfate attack, and freeze–thaw behavior—were not evaluated. Future research incorporating these analyses will strengthen the conclusions, refine technical recommendations for different climatic conditions, and assess the feasibility of applying SCBA and RHA in infrastructure projects with stringent structural and durability requirements.