•Effects of sand, slag and fly ash on microstructure and strength of cemented fillings were studied.•Backfill specimens were manufactured with constant cement (5 wt%) and solid (72 wt%) ...contents.•Among others, 30% sand-based cementitious fillings offered the best mechanical strengths.•Sand-GBS-based backfills supports hydration reactions and prevent fill acidifying in the long-term.•Voids of fine-grained GBS and FA is well filled with sand, improving the strength of fillings.
Cementitious paste/mine backfill (CMB/CPB) is a creative way to proficiently decrease the sum of sulfidic tailings. However, considering them as minor raw material and inadequacies in their gradation, OPC (costly and insufficient)-induced ecological harms, using alternative additives in CMB has become essential. This study aims to increase the short-/long-term filling performance and to reduce cement-related costs by using both sand as tailings substitute, and GBS or FA (granulated blast furnace slag or fly ash) as OPC substitution. Some mechanical (UCS, stress–strain, and modulus of elasticity) and microstructural (MIP, XRD, TG/DTG and SEM) characterization tests for CMBs were experimentally scrutinized. Samples were prepared at diverse curing ages (3–180 days), constant cement/solid content (5/72 wt%), three diverse aggregates (tailings/sand: 100/0, 90/10 and 70/30) and OPC (OPC/GBS-FA: 100/0, 90/10 and 70/30) substitution ratios. Results disclosed that 30% sand-based CMB (S30) offered the best strengths. Besides, strength loss was observed in all 90-day cured backfills, while strength gain was observed in sand/GBS-based backfills up to 180 days. This can be stated by the fact that sand/GBS supports hydration reactions and prevent fill acidifying in the long-term owing to their high CaO contents (sand: ∼54%; GBS: ∼35%). Moreover, improving sand’s gradation, filling the voids of fine-grained GBS and FA is one of the cogent reasons for strength gains. To summarize, this study runs a full report on a cost-effective and viable CMB system that will both make operations profitable/sustainable and prevent environmental damages.
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•This work contains successful prediction and optimization of Portland cement systems.•Novel predictions of heat-evolution profiles were achieved via machine learning (ML).•This work ...offers an original dataset, which contains results for 300+ unique entries.•The database considers mixture design and physiochemical features as attributes.•This work can be expanded to formulate mixture design based on user kinetic-criteria.
The production of ordinary Portland cement (OPC), the most broadly utilized man-made material, has been scrutinized due to its contributions to global anthropogenic CO2 emissions. Thus — to mitigate CO2 emissions — mineral additives have been promulgated as partial replacements for OPC. However, additives — depending on their physiochemical characteristics — can exert varying effects on OPC’s hydration kinetics. Therefore — in regards to more complex systems — it is infeasible for semi-empirical kinetic models to reveal the underlying nonlinear composition-property (i.e., reactivity) relationships. In the past decade or so, machine learning (ML) has arisen as a promising, holistic approach to predict the properties of heterogeneous materials, even without an across-the-board comprehension of the underlying composition-properties correlations. This paper describes the use of a Random Forests (RF) model to enable high-fidelity predictions of time-dependent hydration kinetics of OPC-based systems — more specifically OPC + mineral additive(s) systems — using the system’s physiochemical attributes as inputs. Results show that the RF model can also be used to formulate mixture designs that satisfy user-imposed kinetics-related criteria. Lastly, the presented results can be expanded to formulate mixture designs that satisfy target kinetic criteria, even without knowledge of the underlying kinetic mechanisms.
•The hydration degree of pastes was investigated, using TGA methods.•A modified TG method for calculating the hydration degree was suggested.•The suggested method was validated by hydration heat and ...compressive strength.
Reducing environmental pollution is becoming an important issue that must be taken into consideration, particularly, when producing concrete. Mineral additives used as cement replacement should help in achieving economic performance and ecological pollution reduction. A key question concerning the performance of mineral additives blended cement is the assessment of the contribution of mineral additives to the hydration kinetics. In this paper, the hydration degree of cement pastes containing blast furnace slag and limestone filler was investigated. The investigation was conducted first by using classical thermogravimetric analysis (TGA) methods, which are based on ultimate chemically bound water estimation. A modified TG method based on the direct estimation of the amount of mineral additives contributing to hydration reactions, was then suggested. The accuracy of the suggested method was verified using an isothermal calorimetry test on paste specimens and a compressive strength test on mortar specimens.
This study presents test results and in-depth discussion regarding the measurement of the fracture mechanics parameters of new concrete composites based on quaternary blended cements (QBC). A ...composition of the two most commonly used mineral additives, i.e., fly ash (FA) and silica fume (SF), in combination with nanosilica (nS), has been proposed as a partial replacement for ordinary Portland cement (OPC) binder. Four series of concrete were made, one of which was the reference concrete (REF) and the remaining three were QBC. During the research, the main mechanical parameters of compressive strength (fcm) and splitting tensile strength (fctm), as well as fracture mechanics parameters and the critical stress intensity factor KIcS, along with critical crack-tip opening displacements (CTODc) were investigated. Based on the tests, it was found that the total addition of siliceous materials, i.e., SF + nS without FA, increases the strength and fracture parameters of concrete by approximately 40%. On the other hand, supplementing the composition of the binder with SF and nS with 5% of FA additive causes an increase in all mechanical parameters by approximately 10%, whereas an increase by another 10% in the FA content in the concrete mix causes a significant decrease in all the analyzed factors by 10%, compared to the composite with the addition of silica modifiers only.
3D printing technology revolutionizes construction by creating custom building components with increased efficiency and reduced waste. This paper reviews advancements in the 3D printing of ...cementitious materials, focusing on integrating mineral additives (MAs) like metakaolin, micro-silica, slag, and fly ash to address environmental and economic challenges linked with high-Portland cement content in 3D concrete printing (3DCP). MAs enhance the pumpability, printability, and buildability of 3DCP while reducing its environmental impact. The review emphasizes optimizing cement mixtures, including alkali-activated materials, to enhance sustainability and performance. It discusses the mixture design's importance, balancing mechanical properties and environmental impacts, and examines MAs' influence on rheological properties, mechanical performance, and 3DCP durability, including layer bond strength. The paper also discusses global 3D printing technology adoption in construction and challenges in additive manufacturing implementation. By analyzing printing parameters, mixture proportions, and materials' effects on long-term performance, this review highlights 3D printing's potential for economically viable and eco-friendly structural elements. It aims to guide future advancements in 3D printable cementitious materials, meeting modern construction demands while addressing traditional concrete production's environmental challenges.
•Using recycled mineral additives reduces 3D-concrete printing's environmental impact.•Optimizing printing parameters strengthens layer bonds in 3D-concrete printing.•Recycled materials promote sustainability and innovation in 3D-concrete printing.
•Uncertainty in the hydration process of calcium aluminate cement is eliminated.•New stable phases are formed with the use of microsilica and anhydrite CaSO4.•The long-term strength problem of ...calcium aluminate cement is prevented.•Effects of pre-heating on the strength development of mortars are investigated.
Strength development of Calcium Aluminate Cement (CAC) under various environmental conditions is an interesting subject of topic that pay attention of researchers for a long time. This special cement usually preferred in applications where quick setting ability, high early strength and resistance to chemical attack is required. However, uncertainty in the hydration process and long-term strength problems, due to conversion reactions in combination with high initial material cost, limit the application of this cement.
In order to propose a solution to the above-mentioned problems, blended mortar mixtures were prepared by replacing CAC with variable amounts of microsilica, anhydrite CaSO4 and Portland cement within the scope of this study. The compressive strength development of mortar specimens up to 400 days were investigated under semi-dry curing conditions at 20 ± 5 °C and 60 ± 20% RH. During the initial stages of hydration, a distinct pre-heating based curing procedure was applied to the conjugate specimens. Preliminary stabilization of the unstable hydration products is targeted by this pre-heating method. Accordingly, the crystal structure of the hydration products of specimens was analyzed with the support of microstructural studies (XRD, DTA-TGA, SEM-EDS). The pore size distribution and sub-capillary porosity of specimens were also determined by mercury intrusion porosimetry. The effectiveness of the mineral modification and pre-heating based curing method (exposure to 50 ± 1 °C heating for 21 days) on the long-term strength development of CAC is discussed with the aid of microstructural analysis results. The results showed that it is possible to stabilize the hydration process of CAC and its strength becomes predictable in the long term, if appropriate mineral additives in proper replacement ratios are employed in the mixture design.
•A self-healing system was investigated in different humidity environments.•Excellent healing efficiency was achieved using the self-healing system.•Self-healing system reduced drying shrinkage and ...mechanical strength.•Healing mechanism of the super absorbent polymer under wet-dry cycle was explored.
Super absorbent polymers, which allow better moisture retention within cracks for extended periods, can be beneficial in facilitating the autogenous self-healing process of concrete incorporated with carbonate-built lightweight aggregates. In the present study, the combined effect of super absorbent polymers and mineral additives, the calcium source provider, on the self-healing properties of self-healing lightweight concrete was investigated. In addition to determining the effect on compressive strength and drying shrinkage, a destructive test by flexural strength and a non-destructive test through electrical impedance spectroscopy were conducted to evaluate self-healing efficiency under different curing regimes. The results showed that the strength was increased by adding mineral additives, while it decreased with increasing the dosage and size of super absorbent polymers. In addition, the application of super absorbent polymers has significantly improved the healing efficiency, especially by 56.1% with adding the large size of super absorbent polymers in the wet-dry cycle. Furthermore, through the analysis of electrical impedance spectroscopy, the super absorbent polymers of large particle size were proved to have excellent moisture retention within cracks in the wet-dry cycles. According to microscopic observation, the potential mechanism was proposed that the swollen super absorbent polymers were possible to further improve self-healing efficiency in the wet environment.
•Computer image processing and ultrasonic tests quantified self-sealing of mortars.•The different self-sealing kinetics of mortars with MAFBC fly ash are indicated.•MAFBC fly ash improved the ...adhesion of polypropylene fibers to the cement matrix.•Hydrated calcium aluminates were identified as products of self-healing.•The efficiency of self-healing was affected by the soluble aluminum content.
This study investigates the effect of the modification of cement-based composites with mechanically activated fly ash from lignite combustion in fluidized bed boilers (MAFBC fly ash) on self-healing. The subject of the research was mortar samples in which, after 28 days of maturing, cracks 0 to 750 µm wide were mechanically induced, followed by curing for 152 days. Via computer processing and analysis of high-resolution scanner (HRS) images, the maximum average crack width reduction was determined to be 43%. The analysis of samples via ultrasonic pulse velocity (UPV) measurements estimated the degree of crack filling with newly formed material during self-sealing to be as high as 58%. In terms of mechanical properties, a maximum flexural strength recovery of 54% was observed due to microstructural changes in the contact area between the cement matrix and polypropylene fibers. To examine self-healing at a microstructural level, optical and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) were applied to the surface of cracks and fragments cut out of the samples. The results showed that the use of MAFBC fly ash as a partial substitute for cement led to the modification of the products of self-healing. Hydrated calcium aluminates were observed in the cracks in addition to typical self-healing products. In the interior of the samples, the complete filling of cracks up to a width of 110 µm was observed.
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