Moisture expansion as a deterioration factor for sandstone used in buildings

The expansion processes that develop in building stones upon changes of moisture content may be an important contributing factor for their deteriorations. Until recently, few data could be found in the literature concerning this parameter and weathering processes. Moreover, the processes that may be responsible for the moisture related expansion of natural building stones are not yet completely understood. To further elucidate this process, extensive mineralogical, petrophysical and fabric investigations were performed on eight German sandstones in order to obtain more information regarding the weathering process and its dependence on the rock fabric. The analysed sandstones show a wide range of pore size distributions and porosities. A positive correlation with the fabric and the pore space can be found for all studied petrophysical parameters. The intensity of the expansion and related swelling pressure cannot be attributed only to the swelling of clay minerals. The investigations suggest that the micropores and the resulting disjoining pressure during wet/dry cycles also play an important role. The results obtained suggest that the mechanism is related to the presence of liquid water within the porous material

Synthesis of Zeolites from Fine-Grained Perlite and Their Application as Sorbents

The hydrothermal alteration of perlite into zeolites was studied using a two-step approach. Firstly, perlite powder was transformed into Na-P1 (GIS) or hydro(xy)sodalite (SOD) zeolites at 100 °C and 24 h using 2 or 5 M NaOH solutions. Secondly, the Si:Al molar ratio of the reacted Si-rich solution was adjusted to 1 by Na-aluminate addition to produce zeolite A (LTA) at 65 or 95 °C and 6 or 24 h at an efficiency of 90 ± 9% for Al and 93 ± 6% for Si conversion. The performance of these zeolites for metal ion removal and water softening applications was assessed by sorption experiments using an artificial waste solution containing 4 mmol/L of metal ions (Me(2+): Ca(2+), Mg(2+), Ba(2+) and Zn(2+)) and local tap water (2.1 mmol/L Ca(2+) and 0.6 mmol/L Mg(2+)) at 25 °C. The removal capacity of the LTA-zeolite ranged from 2.69 to 2.86 mmol/g for Me(2+) (=240–275 mg/g), which is similar to commercial zeolite A (2.73 mmol/g) and GIS-zeolite (2.69 mmol/g), and significantly higher compared to the perlite powder (0.56 mmol/g) and SOD-zeolite (0.88 mmol/g). The best-performing LTA-zeolite removed 99.8% Ca(2+) and 93.4% Mg(2+) from tap water. Our results demonstrate the applicability of the LTA-zeolites from perlite for water treatment and softening applications

Using high‐resolution XRF analyses as a sequence stratigraphic tool in a mudstone‐dominated succession (Early Cretaceous, Lower Saxony Basin, Northern Germany)

Delineation of stratigraphic sequences and their component systems tracts in mudstone‐dominated successions is challenging due to the relatively homogenous, fine‐grained nature of the strata. High‐resolution elemental intensity data from X‐ray fluorescence core scanning is used in order to develop a sequence stratigraphic framework for the Lower Cretaceous monotonous mudstone succession in the eastern Lower Saxony Basin. The study is based on four drill cores covering the Berriasian to Aptian interval. In addition, carbon isotope (δ13Corg), grain size and CaCO3 analyses were carried out on discrete samples. The studied cores represent both proximal and distal basinal environments of the eastern Lower Saxony Basin and can be reliably correlated by utilizing variations in selected X‐ray flourescence elemental ratios, K/Ti data have proven to be particularly suitable in this regard. The core correlation shows that chemostratigraphic variability within the studied succession is laterally reproducible in the eastern Lower Saxony Basin, and can be used to establish a sequence stratigraphic framework. Further, Si/Al and Ca/Ti ratios have been applied to characterize the cores in terms of variation in grain size and CaCO3 content, respectively. Vertical grading trends inferred from Si/Al changes were used to identify transgressive and regressive systems tracts within the studied succession. An important regression in the uppermost lower Valanginian coincides with the onset of the Valanginian Weissert Event, as indicated by the well‐known positive δ13C shift, and, thus, supports the idea that the initial interval of this event corresponds to enhanced supply of terrigenous material. The results of this study are also in agreement with previously recognized transgressive–regressive trends in the Lower Saxony Basin and adjacent areas. This clearly shows that systematic geochemical variations recorded in mudstone‐dominated basinal settings are suitable to establish sequence stratigraphic frameworks

Redox cycling of straw-amended soil simultaneously increases iron oxide crystallinity and the content of highly disordered organo-iron(III) solids

Iron speciation in soils is influenced largely by its redox state, but the extent of and controls on Fe speciation during recurrent reduction and oxidation events are not fully understood. To investigate the effects of organic matter (OM) inputs and the frequency and duration of redox oscillations on soil Fe speciation, we conducted redox-oscillation experiments with topsoil from a Fluvisol mixed with rice straw (0, 10, 50 g/kg organic carbon, OC). The soil was initially dominated by short-range ordered (SRO) Fe(III) solids and subjected to 14- and 28-day reduction–oxidation cycles for 112 days, with the time spent under anoxic and oxic conditions maintained at 6:1. Reduction was initiated by flooding reactors with artificial river water. To simulate leaching conditions, soil re-oxidation was achieved by air-drying soil after removal of reacted solutions. Fresh river water was then added for each new redox cycle. We monitored changes in solution composition (Eh, pH, Fe(II), total Fe, OC, and Si) and assessed changes of solid-phase Fe speciation by selective extractions, X-ray absorption spectroscopy, and 57Fe Mössbauer spectroscopy. Dissolved OC and Fe increased with increasing straw addition, but decreased in each treatment through consecutive reduction intervals. Release rates of dissolved Fe and OC were highly correlated, implying that microbial reduction of soil Fe(III) solids was fostered by straw amendments. Reduction-induced losses of OC and Fe from straw amended soil were amplified at high redox frequency. Ferrous Fe did not detectably accumulate in the solid phase upon repeated soil oxidation. Although Fe(III)-poor phyllosilicates gained in relative importance in redox-cycled soils, their fraction was hardly affected during redox cycling. Instead, straw additions led to an enhanced depletion of ferrihydrite during soil redox cycling and a relative enrichment of highly disordered Fe(III) species [‘very SRO (vSRO) Fe(III) solids’], which remained only partially ordered in 5-K Mössbauer spectra and likely consisted predominantly of polynuclear organic Fe complexes. The depletion of ferrihydrite in straw-amended soils after 112 days was greater in the 14-day cycle than in the 28-day cycle experiment and accompanied by a less pronounced enrichment of vSRO Fe(III) solids. The crystallinity of distinct Fe oxides (ferrihydrite, lepidocrocite, and hematite) increased during soil redox cycling especially in straw-amended soils, but without noticeable ferrihydrite conversion into crystalline Fe oxides. The increase in the crystallinity of distinct Fe oxides after 112 days was greater at low redox frequency in straw-free soil, however this frequency effect was suppressed by straw additions. Longer soil redox cycling (112 vs. 56 days) increased the crystallinity of distinct Fe oxides, which was most pronounced at high straw levels and low redox frequency. Our results imply that redox changes in SRO Fe oxide- and OM-rich soils can cause a relative enrichment of more crystalline Fe oxides, while still maintaining a pool of vSRO Fe(III) solids. We conclude that soil redox oscillations can lead to divergent transformation pathways of Fe oxides, which concomitantly increase bulk Fe-oxide crystallinity and generate increasing fractions of highly disordered Fe(III) solids on comparatively short time scales. In addition, our study suggests that faster redox cycling in soils with ample electron donor supply and water leaching leads to higher element exports (e.g., OC, metal(loid)s) from soil due to weekly redox pulsing than more slowly alternating redox conditions

Microbial community dynamics in soil depth profiles over 120,000 years of ecosystem development

Along a long-term ecosystem development gradient, soil nutrient contents and mineralogical properties change, therefore probably altering soil microbial communities. However, knowledge about the dynamics of soil microbial communities during long-term ecosystem development including progressive and retrogressive stages is limited, especially in mineral soils. Therefore, microbial abundances (quantitative PCR) and community composition (pyrosequencing) as well as their controlling soil properties were investigated in soil depth profiles along the 120,000 years old Franz Josef chronosequence (New Zealand). Additionally, in a microcosm incubation experiment the effects of particular soil properties, i.e., soil age, soil organic matter fraction (mineral-associated vs. particulate), O2 status, and carbon and phosphorus additions, on microbial abundances (quantitative PCR) and community patterns (T-RFLP) were analyzed. The archaeal to bacterial abundance ratio not only increased with soil depth but also with soil age along the chronosequence, coinciding with mineralogical changes and increasing phosphorus limitation. Results of the incubation experiment indicated that archaeal abundances were less impacted by the tested soil parameters compared to Bacteria suggesting that Archaea may better cope with mineral-induced substrate restrictions in subsoils and older soils. Instead, archaeal communities showed a soil age-related compositional shift with the Bathyarchaeota, that were frequently detected in nutrient-poor, low-energy environments, being dominant at the oldest site. However, bacterial communities remained stable with ongoing soil development. In contrast to the abundances, the archaeal compositional shift was associated with the mineralogical gradient. Our study revealed, that archaeal and bacterial communities in whole soil profiles are differently affected by long-term soil development with archaeal communities probably being better adapted to subsoil conditions, especially in nutrient-depleted old soils

Porosity and distribution of water in perlite from the island of Milos, Greece

A perlite sample representative of an operating mine in Milos was investigated with respect to the type and spatial distribution of water. A set of different methods was used which finally provided a consistent view on the water at least in this perlite. Infrared spectroscopy showed the presence of different water species (molecular water and hydroxyl groups / strongly bound water). The presence of more than 0.5 mass% smectite, however, could be excluded considering the cation exchange capacity results. The dehydration measured by thermal analysis occurred over a wide range of temperatures hence confirming the infrared spectroscopical results. Both methods point to the existence of a continuous spectrum of water binding energies. The spatial distribution of water and/or pores was investigated using different methods (CT: computer tomography, FIB: scanning electron microscopy including focused ion beam technology, IRM: infrared microscopy). Computer tomography (CT) showed large macropores (20 – 100 μm) and additionally revealed a mottled microstructure of the silicate matrix with low density areas up to a few μm in diameter. Scanning electron microscopy (FIB) confirmed the presence of μm sized pores and IRM showed the filling of these pores with water. In summary, two types of pores were found. Airfilled 20 – 100 μm pores and μm-sized pores disseminated in the glass matrix containing at least some water. Porosity measurements indicate a total porosity of 26 Vol%, 11 Vol% corresponding to the μm-sized pores. It remains unsolved wether the water in the μm-sized pores entered after or throughout perlite formation. However, the pores are sealed and no indications of cracks were found which indicated a primary source of the water, i.e. water was probably entrapped by quenching of the lava. The water in these pores may be the main reason for the thermal expandability which results in the extraordinarily porous expanded perlite building materials