Display omitted
► Calcium carbonate biodeposition method contributed to decrease in water absorption of recycled concrete aggregate. ► Better efficiency was obtained for finer aggregate fraction and ...in the case of aggregate of lower quality. ► Efficiency of calcium chloride and whey as culture media was confirmed. ► Observations under SEM showed covering aggregate grains with calcium carbonate.
A growing demand for raw materials leads to danger of premature depletion of the natural sources. An alternative is to use by-products, provided their quality is improved. The paper presents surface modification of recycled aggregate concrete using biodeposition involving a method employing Sporosarcina pasteurii (Bacillus pasteurii) bacteria. It was possible to obtain reduction in water absorption of aggregate, the effect was more visible in case of finer fractions and for aggregates originating from inferior quality concrete. Calcium chloride was used for precipitation of calcium carbonate, while culture medium consisting of beef extract, peptone and urea was used for cultivation of microorganisms. In addition, whey, ecologically dangerous by-product from dairy industry was found to be effective as a culture medium. Presence of calcium carbonate crystals covering aggregate grains was confirmed by observations under scanning electron microscope. In the perspective, the proposed method, upon appropriate improvements, seems worthwhile due to ecological and technological reasons.
For complete utilization of construction and demolition (C&D) waste, an investigation of all size fractions of C&D waste generated during the recycling process should be conducted. In this work, the ...effects of three recycled concrete materials with different sizes (recycled coarse aggregate (RCA) with a size of 4.75-25 mm, recycled fine aggregate (RFA) of 0.15-4.75 mm, and recycled powder (RP) smaller than 0.15 mm) produced from concrete waste on the fresh and hardened mechanical properties of concrete were evaluated. The replacement ratios of natural coarse and fine aggregates by RCA and RFA were 30, 60, and 100%, and those of ordinary Portland cement for RP were 10, 20, and 30%. The results showed that the concrete properties deteriorated with increasing replacement ratio regardless of the type of recycled materials. The properties were reduced in the order of the use of RFA, RCA, and the simultaneous use of RCA and RFA. In addition, concrete with 30% RP showed lower mechanical strength than concrete with 100% RCA and 100% RFA. However, all concretes could be applicable for structural purposes under different environmental exposure conditions. In particular, concretes with 10% RP and 20% RP showed better cost-benefits compared to natural aggregate concrete with 100% ordinary Portland cement. These promising findings provide valuable initiatives for the effective and complete recycling of C&D waste.
The decrease in the quality of recycled aggregate due to an increase in the number of recycling is a primary factor that limits the multi-recycling of concrete. This degradation adversely affects ...concrete performance; thus, the characteristics of recycled aggregate should be considered during the mix design stage, but little research has taken that into account. This study investigates the effect of the equivalent mortar volume (EMV) mix design on some physical, mechanical and durability properties of concrete made of multiple recycled coarse aggregates at 50% and 100% replacement ratios compared to concrete made by the conventional mix design (CMD). The results showed that the performances of concrete by the CMD decreased with an increasing number of recycling cycles. The properties of EMV-based concrete deteriorated with an increase in the number of recycling cycles at 100% replacement ratio due to poor workability caused by a shortage of fresh mortar. However, at 50% replacement, the EMV-based concrete exhibited similar performance across the three cycles of recycling, as well as improved properties over natural aggregate concrete. This study demonstrated that an appropriate mix design and optimal aggregate replacement ratio can offset the property loss of multiple recycled aggregate concrete.
•Influence of type and size of aggregate and pozzolana cement on HSC was determined.•0/8mm aggregate with cement at 700 instead of 600kg/m3 improved strength by 8.5%.•In case of 0/16mm aggregate ...there was no need to increase cement amount to 700kg/m3.•Basalt or granite of 0/16mm size and 600kg/m3 of cement curbed HSC carbon footprint.
In compliance with up-to-date concrete technology requirements combining technological and ecological aspects, the paper describes the effect of the type and maximum aggregate size and cement content on some properties of high strength concrete. The following kinds of coarse aggregate were used to produce concrete: natural mineral (gravel) and crushed (granite and basalt) aggregates and pozzolana cement – ingredient classified as ecological binder. The concretes contained a highly effective superplasticiser and microsilica. Air content in concrete mixes, water absorption and concrete compressive strength after various periods of hardening were examined. Certain calculations (based on compressive strength results) on values of intensity indexes of cement used and carbon dioxide, treating them as a key for evaluation of eco-efficiency of concrete, were performed. Using pozzolana cement with simultaneous use of a highly effective superplasticiser and microsilica made it possible to obtain high strength concrete, made of mineral natural and crushed aggregates. More encouraging strength tests results were achieved for concrete of crushed aggregates, particularly granite. It was discovered that using aggregate with a maximum particle size less than 8mm instead of aggregate with particles measuring up to 16mm with a simultaneous increase in the cement content led to a greater rise in concrete strength. The smallest indexes of binder and carbon dioxide intensity were obtained as a result of use of granite and basalt aggregate, with a maximum particle size up to 16mm.
The paper is focused on the eco-efficiency calculations of recycled aggregate concrete (RAC) consisted of ordinary Portland and blast-furnace slag cements with three fine-grained wastes: quartz ...powder (Q), limestone powder (L) and fly ash (F). The characteristics of concrete mixes (slump and air content) and hardened concrete properties: 28- and 90-day compressive strength, water absorption as well as the depth of the carbonation (after the accelerated carbonation in the chamber) were examined. In order to parameterize the third feature of contemporary concrete, which is (next to the strength and durability) its sustainability potential, the binder intensity (bi) and carbon intensity (ci) indexes were calculated, taking into account CO2 emissions from cement production and technological processes related to preparation for use of other ingredients. The comparison of the effect of limestone powder and fly ash showed some advantages of the fly ash (taking into account the results of strength tests). However, limestone powder turned out to be more favorable in influencing other properties (especially resistance to carbonation). Nevertheless, the use of fly ash proved to be the most effective in terms of eco-efficiency factors. The pozzolanic properties of F increased the strength of the concrete, reducing both bi and ci values. Furthermore, the presence of F canceled out the negative effect of quartz powder. The use of F together with cement containing ground-granulated blast-furnace slag (GGBS) was most beneficial. Although quartz powder due to technological reasons occurred to be the worst option, its use may be beneficial when CO2 sequestration by concrete carbonation is taken into account. Lower strength and resistance to carbonation of concrete with Q allow CO2 to penetrate deeper into the structure, especially in concrete made of GGBS cement. In this way, the later uptake of CO2 from the atmosphere allows for a partial reduction of the ci value, making RAC more eco-efficient.
•The effects of quartz powder (Q), limestone (L) and fly ash (F) on RAC were tested•F increased compressive strength, L gave better slump and lower permeability•Q achieved the worst results, but in combination with L or F situation is improved•F considerably improved eco-efficiency, especially for RAC with GGBS cement•Use of Q may be beneficial if CO2 sequestration via carbonation is a priority
The paper presents the influence of different curing conditions—wet, dry, and protection against water evaporation (PEV)—on selected properties of concretes with different amounts of recycled ...concrete aggregate (RCA) previously subjected to atmospheric CO2 sequestration. Two types of cement were used, Portland cement and blast-furnace slag cement. The study was performed in laboratory conditions (at the temperature of 20 ± 1 °C and relative humidity of about 60%), according to currently applicable test procedures for most of the measured characteristics of concrete. Additionally, the eco-efficiency indexes (bi and ci) as well as the eco-durability S-CO2 index were calculated. It was found that dry conditions cause the properties of concrete to deteriorate, especially concrete made of blast-furnace slag cement, while PEV allows the achievement of results comparable to wet conditions. Moreover, for series with the highest amounts of coarse recycled aggregate and after longer periods of curing, the difference between the effects of wet curing and protection against water evaporation disappears. The eco-efficiency and eco-durability indexes approach confirms the beneficial effect of blast-furnace slag cement used as a binder, but on the condition of using a proper way of curing.
Urban furniture is a wide collection of objects of different sizes and geometries, performing different functions in the city. The paper describes the history and contemporary development trends of ...urban furniture. It analyses the construction materials most often used in their production, as well as functional and aesthetic solutions. A questionnaire survey, exploring the issue of urban furniture from the view point of the student population, was statistically analysed. It showed the preferences and expectations of current and future users of urban furniture, which can be helpful in achieving harmony between the creation of a positive image of the city and the comfort of public spaces for its residents. In the study of the preferences of urban furniture users, contingency tables were used for questions with a possible single answer. The results of questions with possible multiple answers were illustrated using Venn diagrams or equivalent UpSetR charts.
Research on recycled concrete aggregates (RCAs) has been progressively advanced. Beyond replacing natural aggregates with RCA, discussions have been held on the effect of the parent concrete and ...repeatedly recycled aggregate concrete. Although it has been reported that RCA can be technically used for structural concrete, due to several other factors, RCA is mainly used for sub-bases. Therefore, identifying these factors is the key to promoting the use of RCA. Therefore, this review study first briefly summarizes the physical and chemical characteristics of RCA compared to natural aggregate, and reviews the effects of parent concrete and repeatedly recycled aggregate on next generation concrete. This study also briefly discusses the RCA standards of various countries and the factors that hinder the widespread use of RCA. The results show that there is a correlation in properties between parent concrete and the next generation concrete, and the properties of concrete decrease when RCA is used repeatedly. In addition, on the basis of the literature review, factors hindering the use of RCA were found to be unstable supply and demand, economic feasibility, and negative perceptions.
Display omitted
•Sporosarcina pasteurii strain ensures lithification and increase of soil rigidity.•Biodeposition highly improves shear strength of silty soil at small deformations.•Sporosarcina ...pasteurii strain is resistant to dynamic impact typical for earthworks.•Observed strengthening effect may be applicable in building earth structures.
Contemporary challenges and results of the research to date show that the search for environmentally-friendly ways of soil improvement is the right direction. The paper presents biogrouting of silty soil compacted using standard energies in the laboratory soil compactor. An improvement of transition soils by biodeposition using Sporosarcina pasteurii has been undertaken. Biodeposition has increased shear strength in the triaxial compression test. It has been concluded that application of bacteria solution on the soil ensures lithification and a significant increase of soil rigidity. Resistance of Sporosarcina pasteurii strain to dynamic impact during soil compaction allows a possible application of these microorganisms in geoengineering.
Contemporary solutions in concrete technology are varied, and consist in e.g. the use of new generation concretes, including the most spectacular achievement of the 1990s – self-compacting concrete ...(SCC) being the subject of continuous research, as well as protection of the environment against excessive anthropogenic pressures, such as carbon dioxide which is a major emission substance from the cement industry. The studies analysed the possibilities for replacing part of the clinker binder (cement CEM I 42.5 R) in self-compacting concrete with three types of waste mineral additives: fly ash, limestone powder, and granite powder. Focus was placed on key technological characteristics of concrete mixes: air content and rheological properties, maximal diameter of slump-flow and changes thereof over time, as well as the mix’s flow time into the 500 mm diameter, determining the flow dynamics. 28-day compressive strength of the concrete was recognised as a secondary property which in self-compacting concretes results from achieving the right range of the mix’s rheological properties. Concretes were produced using gravel-sand aggregate in 3-fraction composition and a high-efficiency superplasticiser. The studies were conducted as a planned experiment in the 3-ingredient mixes plan.
PDF
