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Multiscale assessment of construction and demolition waste aggregates stabilization through alkaline activation
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Compaction and freeze-thaw degradation assessment of recycled aggregates from unseparated construction and demolition waste
No full textAlthough previous studies attested to the feasibility of using recycled aggregates from unseparated construction and demolition waste (UCDW aggregates) in unbound layers of road pavements, the degradation caused by compaction and freezing action under simulative conditions has not been investigated yet. To investigate the effects of these two sources of degradation on resilient modulus (RM), three UCDW aggregates were collected from different plants in the Turin area and compared with a natural (NAT) aggregate. Partially-saturated specimens of UCDW aggregates at the optimal moisture content (wopt) and at wopt±2% were prepared at the gyratory shear compactor with 30 and 100 gyrations, and by subjecting specimens to 0, 4 and 8 two-day freeze-thaw cycles from −18 °C to +20 °C. Brittle and weak components of UCDW aggregates (crushed concrete, bricks) generate fine particles in the first part of the compaction process (in the first 30 gyrations). Freeze-thaw action led to a clear increase in the resilient modulus of UCDW specimens compacted at wopt and wopt+2%. A similar trend in RM was observed in the case of NAT aggregate in similar moisture conditions, while both UCDW and NAT exhibited a slight decrease for some samples prepared at wopt−2%. Under more severe but non-simulative testing conditions such as those currently used to select conventional granular materials, UCDW aggregate exhibits lower performances than NAT aggregate. Conversely, when evaluated in more simulative test conditions, the behaviour of UCDW aggregate is comparable to that of NAT one
Stabilising CDW recycled aggregates with alternatives to Portland cement
Full text linkThe use of ordinary Portland cement for the stabilisation of granular materials in road construction undermines the effort on sustainability made by using recycled aggregate in substitution of natural ones. This requires the use of low-impact binders so that the road construction industry complies with the prevailing environmental regulations. This study compares the mechanical and environmental properties of construction and demolition waste (CDW) aggregates stabilised with different binders: (i) a Portland-limestone cement as a reference, (ii) a pozzolanic cement, (iii) an experimental pozzolanic cement containing waste clay from the lightweight aggregate production, and (iv) a binder with alkali-activated CDW fines. In the laboratory experiments, both strength and resilient properties were considered, while the environmental impact was assessed in a cradle-to-gate scenario through a life cycle analysis (LCA). The stabilised mixture with pozzolanic cement achieved comparable strength and stiffness while exhibiting a lower environmental impact than the mixture containing Portland-limestone cement. The addition of waste clay to the pozzolanic cement significantly reduces its environmental impact albeit more binder is required to compensate for the lower mechanical properties. The alkaline activation of the fine particles in the CDW aggregate enabled the creation of a stabilised mixture with high strengths and resilient modulus. However, this alternative stabilisation technique requires further optimisation to mitigate the significant environmental impact. The engineering evaluations of the stabilised granular mixtures studied have considered both mechanical and environmental factors intending to contribute to the scientific debate on how to make roadworks sustainable and conserve natural resources
Short-Term and Long-Term Effects of Cement Kiln Dust Stabilization of Construction and Demolition Waste
Full text linkHigh volumes of construction and demolition waste (CDW) are continuously produced worldwide. The European Commission aims to increase the recycling of nonhazardous CDW to a minimum of 70% in weight terms by 2020. Hence, there is increasing pressure on researchers to focus on the valorization of these alternative materials for use in the world of construction alongside traditional materials. CDW contains materials from excavation and/or demolition and are typically heterogeneous in terms of composition, grain size, and toughness; furthermore, some particles are more sensitive to degradation processes than others. One solution for an increase in durability while maintaining sufficient strength levels is chemical stabilization with cementitious binders. The paper illustrates the results of a laboratory investigation into the properties of CDW when subject to stabilization with cement kiln dust (CKD). Mixtures of CDW stabilized with ordinary portland cement (OPC) were prepared for comparison purposes. The results obtained with CKD are encouraging because it increases the strength and stiffness of CDW, thus leading to a material completely made up of recycled wastes and by-products usable in the formation of pavement subbases and subgrades. As regards the curing time, all mixtures saw a significant increase in their mechanical parameters when passing from 7-28 days to 365 days of curing
Use of Cement Kiln Dust to Stabilize Construction and Demolition Waste for Pavement Applications
No full textHigh volumes of construction and demolition waste (CDW) are continuously produced worldwide. The European Commission aims to increase the recycling of non hazardous CDW to a minimum of 70% in weight terms by 2020. Hence, there is increasing pressure on researchers to focus on the valorization of these alternative materials for use in the world of construction alongside traditional materials. CDW contains materials from excavation and/or demolition and are typically heterogeneous in terms of composition, grain size, and toughness; furthermore, some particles are more sensitive to degradation processes than others. In order to increase durability while maintaining sufficient strength levels, one solution consists of chemical stabilization with cementitious binders. The paper illustrates the results of a laboratory investigation into the stabilization of CDW using cement kiln dust (CKD). Compared to ordinary Portland cements, CKD exhibits a weak binding attitude due to the limited content of oxides; hence, it has to be employed in larger quantities. The results obtained with the use of CKD are encouraging since it increases the strength and stiffness of CDW, thus leading to a material completely made up of recycled wastes and by-products usable in the formation of pavement subbases and subgrade
The effect of specimen size on the unconfined compressive strength of cement-stabilized granular mixtures made of natural and recycled aggregates
Full text linkMechanical properties, life-cycle assessment, and costs of alternative sustainable binders to stabilise recycled aggregates
Full text linkCement-stabilised subbases provide superior bearing capacity and durability to road pavements compared to unbound aggregate layers. However, stabilisation reduces the environmental benefits derived when recycled aggregates are used. This research compares alternative binders to Portland cement to highlight mechanical, environmental, and economic advantages and disadvantages in a cradle-to-production scenario. Three low-clinker cements with different proportions of pozzolana and three alkali-activated (AA) binders derived from (i) construction and demolition waste fines, (ii) municipal incinerator bottom ash and (iii) waste clay, were compared to Portland limestone cement. The compressive strength of binder pastes was measured after 7 and 28 curing days.
Pozzolanic cements proved viable alternatives to Portland ones, while AA pastes exhibited lower strengths. The crystallinity of alkali-activated silica- and alumina-rich waste precursors was responsible for their limited strength. The life cycle assessment indicated that the replacement of clinker with pozzolana significantly reduces the environmental impact. AA binders with waste precursors can reduce the environmental impact only with a limited quantity of alkaline solution. If the lower strength achieved by AA binders is compensated by adding higher quantities to recycled aggregate, the increase in environmental impact and cost would make them less competitive. The option of using AA binders would be further strengthened with the production of environmentally friendly alkaline solutions and greater local availability of amorphous precursors. At present, cements are cheaper than AA binders due to the current massive production, widespread availability, and competition between producers
Preliminary laboratory multi-scale investigation on performance of pervious concrete pavements and vegetated elements as storm water bio-filters and retention systems
Full text linkThe growing population in urban areas worldwide is having a severe impact on the environment and quality of life of inhabitants. To alleviate the impact on traditional transportation infrastructures, existing and future urban facilities must be more environmentally friendly and sustainable. One solution is to develop new “green transportation infrastructures” (GTI) as part of the urban storm water management system.
Although technologies for GTI have been well-investigated, there is limited experience of their potential benefits globally and, specifically, in Italy. This work, funded by the Regione Piemonte in 2015 and supported by different areas of expertise, aimed at promoting new urban storm water systems through the retention, filtration, and restoration of natural soil water content.
To this end, a laboratory investigation of porous road pavements (Figure 1), and vegetated boxes (Figure 2 and 3) that filter runoff pollutants from impervious pavements was conducted to examine ecological, hydraulic, and mechanical performance levels.
Three different experimental scales (samples, columns, and boxes) for the two GTI technologies were considered. Samples were used to assess the permeability, void content, strength, and pollution reduction potential of different materials used to build full-scale bio-filter systems. The pollutant reduction was determined by the reduction in suspended solids and hydrocarbon concentration, with results confirming that it depends on filter type and permeability. The preliminary results are encouraging and show a high reduction in total suspended solids and hydrocarbon concentrations (from 65% to 99%).
Concrete pervious pavements and vegetated bio-filter systems were reproduced in columns and boxes, combining materials and supports for biofilm bacteria (geotextile, plastic caps) to assess the abatement potential of pre-developed biofilm bacteria compared to systems where bacteria are present naturally. Hydraulic parameters (percolation time, void content, outflow rate) were estimated so as to provide basic design parameters for full-scale applications
High Albedo Interlocking Concrete Block Pavement for Urban Heat Island Mitigation
No full textThe combined effects of global warming and urbanisation have intensified the urban heat island (UHI) phenomenon and thermal stress, especially in the summer season. This study develops an integrated multi-scale framework to quantify the sustainability in terms of the thermal performance of high albedo interlocking concrete block pavement (ICBP) in the city of Turin, Italy. The framework combines: (1) experimental campaigns to establish baseline albedo values, using an albedometer (in accordance with the standard ASTM E1918-21 and E1980-24); (2) in situ measurements to assess the performance of ICBP in three parking areas; (3) satellite analysis using Landsat 8-9 and Sentinel-2 images to derive the land surface temperature (LST) and quantify changes in the surface urban heat island intensity (SUHII). In situ measurements showed an average albedo of 0.20 for ICBP, lower values for aged surfaces and about 0.08 for asphalt. Satellite analysis confirmed the effectiveness of the substitution of asphalt surface pavements with ICBP, revealing an increase of over 30% in both the average albedo and the solar reflectance index (SRI). These results are also combined with the 15% decrease in SUHII. Combining on-site measurements and satellite analysis provides a comprehensive framework for quantifying surface urban heat island effects and thermal performances of more sustainable road pavements. These findings support high albedo ICBP as an effective strategy for UHI mitigation
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