In the reinforcement of micro-cracks and soil, cement grouting often suffers from poor injectability due to particle size limitations. While ultra-fine cement produced through physical grinding can address this issue, it significantly increases cost and energy consumption. Moreover, ultra-fine cement is prone to aging when exposed to moisture and CO2 in the air. To address these issues, this study proposes a new approach for in-situ particle size reduction of cement slurry through the mild corrosion of acetic acid. The refining effect of acetic acid on cement particles was investigated, along with its impact on mechanical properties and hydration products. The results show that acetic acid accelerates cement dissolution, promoting early-stage strength development and microstructure formation. The addition of 1.2 wt% acetic acid reduced the D90 particle size of the slurry by 36.4 %. Acetic acid also enhances the release of Ca2+ from clinker, increasing the precipitation of Ca(OH)2, CaCO3, and calcium silicate hydrate (C-S-H) at early stages, which serves as the primary source of early strength. Additionally, it raises the Ca/Si ratio of the early-formed C-S-H gel. However, excessive acetic acid can inhibit the further development of strength at later stages. The research demonstrates that premixed acetic acid activation is an effective approach for enhancing the performance of cementitious grouting materials, with promising potential to reduce energy consumption associated with physical cement grinding.
Fluorite (CaF2) leaching and weathering (30 days) were conducted to measure fluoride dissolution in semiarid endemic soil and controlled synthetic solutions, and determining the main chemical species involved in these processes via atomic force microscopy (AFM), X-ray diffraction (XRD) and Scanning electron microscopy (SEM-EDS). Ecological health response in this system was assessed exposing Allium cepa bulbs to 10, 50, 100, 450, 550 and 950 mg CaF2 kg-1 soil to determine genotoxic damage, protein and systemic fluorine concentrations. Results indicated 3 cycles of passive-active fluorite dissolution enabling fluoride concentrations up to 164 mg L-1 under endemic conditions; however, highest fluoride dissolution was 780 mg L-1 for synthetic sulfates solution. Cyclic behavior was associated with the formation of ultrafine-sized calcite (CaCO3)-like compounds. Fluorine concentrations ranged from 5 to 300 mg kg-1 in vegetable tissue. The electrophoretic profiles revealed changes in the protein expression after 7, 15 and 25 days of exposure. Genotoxic damage rate was 50, 82 and 42% for these exposures (950 mg CaF2 kg-1 soil). The dose-response curves of the normalized total protein content revealed the kinetics vegetable health damage rates for only 7 and 25 days. This behavior was best adjusted for only 7 days. These findings exhibited characteristics for initial damage and adaptation-recovery stage after 15 days. Environmental implications of these findings were further discussed.
During the improvement and reinforcement of peat foundation soils, cement hydration alters the pH of the subsurface water-soil ecosystem. This change negatively impacts humus acid, the main component of organic matter in peat soils, thereby deteriorating the engineering properties of peat foundations. Tests simulated the subsurface alkaline environment by using cement treat peat soils in actual projects. The objective is to understand the dynamic processes of cement hydration affecting peat environments and to investigate the dissolution properties of humus acid in peat soil under alkaline environment during cement hydration. Results indicate that peat soil environment transforms into an alkaline environment under cement hydration, where humus acid in peat soil exhibits dissolution properties under alkaline environment. Humus acid undergoes dissolution and reacts in alkaline environment. As the pH of the environment stabilizes, the dissolution of humus acid practically ceases. As humus dissolves, the pores inside peat soil expand, and the skeleton structure becomes less compact, reducing the soil's compactness connectedness, leading to significant strength loss. The dissolution of humus acid can significantly damage the peat soil structure. study provides valuable insights into engineering issues arising from humus acid dissolution in peat soil under alkaline environment induced by cement hydration.
Despite early hydrological studies of 234U/238U in groundwaters, their utilization as a paleoclimatic proxy in stalagmites has remained sporadic. This study explores uranium isotope ratios in 235 datings (230Th) from six stalagmites in Ejulve cave, northeastern Iberia, covering the last 260 ka. The observed 234U enrichment is attributed to selective leaching of 234U from damaged lattice sites, linked to the number of microfractures in the drip route and wetness frequency, which under certain conditions, may result in the accumulation of 234U recoils. This selective leaching process diminishes with enhanced bedrock dissolution, leading to low S234U. Temperature variations significantly influence bedrock dissolution intensity. During stadial periods and glacial maxima, lower temperatures likely reduced vegetation and respiration rates, thereby decreasing soil CO2 and overall rock dissolution rates. This reduction could enhance the preferential leaching of 234U from bedrock surfaces due to lower bulk rock dissolution. Additionally, the temperature regime during cold periods may have facilitated more frequent freeze-thaw cycles, resulting in microfracturing and exposure of fresh surfaces. Conversely, warmer temperatures increased soil respiration rates and soil CO2, accelerating rock dissolution rates during interstadials and interglacials, when low S 234 U is consistent with high bedrock dissolution rates. The contribution of a number of variables sensitive to bedrock dissolution and wetness frequency processes successfully explains 57% and 74% of the variability observed in the S 234 U in Andromeda stalagmite during MIS 3-4 and MIS 5b-5e, respectively. Among these variables, the growth rate has emerged as crucial to explain S 234 U variability, highlighting the fundamental role of soil respiration and soil CO2 in S 234 U through bedrock dissolution. I-STAL simulations provides the potential for a combination of Prior Calcite Precipitation (PCP) indicators like Mg/Ca with PCP- insensitive indicators of bedrock dissolution such as S234U, along with growth rate data, may be useful to diagnose when PCP variations reflect predominantly changes in drip intervals and when changes in bedrock dissolution intensity contribute. The relationship between stalagmite S234U, bedrock dissolution, and initial dripwater oversaturation suggests two significant advancements in paleoclimate proxies. First, S 234 U could serve as a valuable complement to S13C since it is significantly influenced by soil respiration and soil CO2, thereby reflecting soil and vegetation productivity sensitive to both humidity and temperature. Secondly, since PCP does not fractionate uranium isotopes, S 234 U could be used in combination with Mg/Ca or S44Ca to deconvolve PCP variations due to changing drip rates from those due to changes in initial saturation state. This study emphasizes the overriding climatic control on S234U, regardless of the absolute 234U/238U activity ratios among samples and their proximity or distance from secular equilibrium, and advocates for its application in other cave sites.
Construction spoil (CS), a prevalent type of construction and demolition waste, is characterized by high production volumes and substantial stockpiles. It contaminates water, soil, and air, and it can also trigger natural disasters such as landslides and debris flows. With the advent of alkali activation technology, utilizing CS as a precursor for alkali-activated materials (AAMs) or supplementary cementitious materials (SCMs) presents a novel approach for managing this waste. Currently, the low reactivity of CS remains a significant constraint to its high-value-added resource utilization in the field of construction materials. Researchers have attempted various methods to enhance its reactivity, including grinding, calcination, and the addition of fluxing agents. However, there is no consensus on the optimal calcination temperature and alkali concentration, which significantly limits the large-scale application of CS. This study investigates the effects of the calcination temperature and alkali concentration on the mechanical properties of CS-cement mortar specimens and the ion dissolution performance of CS in alkali solutions. Mortar strength tests and ICP ion dissolution tests are conducted to quantitatively assess the reactivity of CS. The results indicate that, compared to uncalcined CS, the ion dissolution performance of calcined CS is significantly enhanced. The dissolution amounts of active aluminum, silicon, and calcium are increased by up to 420.06%, 195.81%, and 256.00%, respectively. The optimal calcination temperature for CS is determined to be 750 degrees C, and the most suitable alkali concentration is found to be 6 M. Furthermore, since the Al O bond is weaker and more easily broken than the Si O bond, the dissolution amount and release rate of active aluminum components in calcined CS are substantially higher than those of active silicon components. This finding indicates significant limitations in using CS solely as a precursor, emphasizing that an adequate supply of silicon and calcium sources is essential when preparing CS-dominated AAMs.
Carbonate minerals are ubiquitous in nature, and their dissolution impacts many environmentally relevant processes including preferential flow during geological carbon sequestration, pH buffering with climate-change induced ocean acidification, and organic carbon bioavailability in melting permafrost. In this study, we advance the atomic level understanding of calcite dissolution mechanisms to improve our ability to predict this complex process. We performed high pressure and temperature (1300 psi and 50 degrees C) batch experiments to measure transient dissolution of freshly cleaved calcite under H2O, H+, and H(2)CO(3)(-)dominated conditions, without and with an inhibitory anionic surfactant present. Before and after dissolution experiments, we measured dissolution etch-pit geometries using laser profilometry, and we used density functional theory to investigate relative adsorption energies of competing species that affect dissolution. Our results support the hypothesis that calcite dissolution is controlled by the ability of H2O to preferentially adsorb to surface Ca atoms over competing species, even when dissolution is dominated by H+ or H2CO3. More importantly, we identify for the first time that adsorbed H+ enhances the role of water by weakening surface Ca-O bonds. We also identify that H2CO3 undergoes dissociative adsorption resulting in adsorbed HCO3- and H+. Adsorbed HCO3- that competes with H2O for Ca acute edge sites inhibits dissolution, while adsorbed H+ at the neighboring surface of CO3 enhances dissolution. The net effect of the dissociative adsorption of H2CO3 is enhanced dissolution. These results will impact future efforts to more accurately model the impact of solutes in complex water matrices on carbonate mineral dissolution.
Globally, a large amount of phosphogypsum (PG) is produced every year. Most of the PG is stored directly without any treatment, posing a serious threat to the local soil, groundwater and human health. Current researches on the distribution of PG field posllution are all aimed at the surface soil, few studies focused on the distribution of contaminants in the soil under PG. This study used geochemical methods, Pearson'ss correlation analysis, principal component analysis and hierarchical clustering method to analyse the contaminant distribution characteristic in underground soil. This study found that contaminants in the soil can be classified into two categories. Fluoride, total phosphorus, sulfate, Cd, and Hg are one category, and Cu, Pb, As, Cr, Al, Fe, Ni, Zn, and Ba are another category. Each category of contaminants has the same source or similar physical and chemical behaviour, which can be more targeted for future site remediation. Based on the analysis of the mineral composition of the soil, it is found that a large part of the contaminants in the groundwater are caused by the strong acidity of the site. Therefore, the management and control of such acidic sites should pay more attention to the pH status of the site to avoid the release of more contaminants from the site.