Influence of Rheological Active Additives on the Properties of Self-compacting Concrete

The effect of rheological-active additives on the properties of cement suspensions and self-compacting concrete mixtures have been studied.In order to increase the rheological matrix and provide high fluidity,stone powders were used during the crushing of local mountain rocks in self-compacting concrete.Taking into account the high dispersion of rheological-active additives,highly effective plasticizers were used to regulate the reotechnological properties of cement-based mixtures.The effect of sulfonaphthalen-formaldehyde oligomer and polycarboxylate-based hyperplasticizer on rheological properties of cement systems as plasticized additive on methodology proposed by V Kalashnikov was evaluated.The flow rate of cement suspension is determined by means of mini-viscosimeter,spreading of cement-sand mortar by means of Hegermann cone,and the slump of concrete mixture by means of Abraham’s cone.On the basis of obtained results,it was determined that limestone powder was more efficient than other stone powders.Thus,when adding 40%limestone powder to the mixture,the compressive strength of the samples taken from self-compacting concrete mixture increases by 15%-30%compared to the control samples.The optimal quantities of rheological-active additives and plasticizers have been identified and the possibility of obtaining high-strength self-compacting concrete based on them has been confirmed.

Influences of anion concentration and valence on dispersion and aggregation of titanium dioxide nanoparticles in aqueous solutions

Dispersion and aggregation of nanoparticles in aqueous solutions are important factors for safe application of nanoparticles. In this study, dispersion and aggregation of nano-TiO2 in aqueous solutions containing various anions were investigated. The influences of anion concentration and valence on the aggregation size, zeta potential and aggregation kinetics were individually investigated. Results showed that the zeta potential decreased from 19.8 to-41.4 mV when PO4^（3-） concentration was increased from 0 to 50 mg/L, while the corresponding average size of nano-TiO2 particles decreased from 613.2 to 540.3 nm. Both SO4^（2-） and NO3^-enhanced aggregation of nano-TiO2in solution. As SO4^（2-） concentration was increased from 0 to 500 mg/L, the zeta potential decreased from 19.8 to 1.4 mV, and aggregate sizes increased from 613.2 to 961.3 nm.The trend for NO3^- fluctuation was similar to that for SO4^（2-） although the range of variation for NO3^- was relatively narrow. SO4^（2-） and NO3^-accelerated the aggregation rapidly, while PO4^（3-） did so slowly. These findings facilitate the understanding of aggregation and dispersion mechanisms of nano-TiO2 in aqueous solutions in the presence of anions of interest.

Variable retention forestry in European boreal forests in Russia

We explored whether,and to what extent,variable retention(VR)forestry has been applied in European boreal forests in northwestern Russia.Our survey revealed VR since 1910.Between 1910 and the 1960s,the statistics showing how much was retained are largely missing.However,for example,in the 1950s,on a large scale in the Republic of Karelia,up to 200-ha-sized harvesting areas,18–33%,were retention patches with a mean growing stock of 30–40m3 ha−1.In the fellings defined as“incomplete clear fellings,”which were the most common final felling type at that time,11–40%of the growing stock was left.Between the 1960s and the early 1990s,with more efficient harvesting and skidding techniques,conventional clear fellings with a much lower amount of retention were practiced.Concern about the regeneration of harvested areas gradually led to smaller(maximum 50 ha)harvesting areas and the increase of silvicultural activities.Until now,to ensure natural regeneration,patches of understory and 20–25 seed trees(i.e.,ca.15–25m3)per ha have been left permanently in harvesting areas.Landscape-scale retention for protecting ecosystem functions and biodiversity was legislated in 1978 by preserving key biotopes up to 1000 ha in size.Since 2001,promoted by forest certification,the key biotopes,such as paludified forest patches,buffers around water bodies,and habitats of red-listed species,have also been retained in harvesting areas,together with a dispersed retention of different elements.Quantitative estimates of the amount of key biotopes are largely missing.However,estimates of 1–13%in harvesting areas and 23%in whole managed landscapes have been given.VR applied during the last century has emulated natural disturbances and created diverse uneven-aged forest structures with high amounts of diverse coarse woody debris.We conclude that an analysis of past and current retention practices is essential for estimating the global role of Russian forestry.Further decisions on the general direction of Russian forestry and,specifically,retention practices are important to address the global challenges of biodiversity loss and climate change.