In an increasingly competitive economy, we are facing fierce competition in the construction materials industry, where the use of recyclable waste from demolitions has become more than a necessity. The compensation for the loss of certain properties, which could otherwise lead to a reduction in mechanical characteristics, has been achieved through the addition of nanoparticles with superior qualities. This paper will present the main nanoparticles introduced as subtle additives (ranging from 0.01 percent to a maximum of 1 percent) - currently limited due to manufacturing costs - into the formulations of construction materials such as nanocomposites, nanomortars, nanoconcretes, etc., as well as in sometimes substantial fractions of recycled aggregates, among others. Several types of nanoparticles will be discussed, starting with nanoclay, which improves strength and durability and carbon nanotubes, predominantly used in polymers for construction. In concrete, nano-silica can enhance compressive strength and reduce permeability, graphene oxide can improve mechanical properties and reduce weight and nano-metakaolin, being a pozzolanic material, contributes to long-term strength and durability. At the same time, an analysis will be conducted on some of the recyclable waste from construction, which, under certain conditions, can become integral parts of the formulations for new materials. In this way, we can address two societal issues: the first related to recycling demolition waste and the second to reducing pollution. Furthermore, we can highlight the circular economy, as these materials are reintroduced and repurposed in the creation of new advanced building materials.

This study investigates the synergistic influence of multi-walled carbon nanotubes (MWC-NTs), nanosilica powder (NSP), and polypropylene fiber waste (PFW) on the mechanical performance of mortar incorporating demolished concrete waste aggregates (DCWA). The replacement of natural aggregates with DCWA typically results in strength reductions and weak interfacial transition zones; therefore, the combined use of nanomaterials and microfibers is proposed as a mitigation strategy. A Taguchi Design of Experiments (DOE) approach was employed to optimize mix parameters, including MWCNT dosage, NSP content, PFW volume fraction, and DCWA replacement level. Mortar mixtures were prepared with MWCNTs (0–0.1% by binder weight), NSP (0–2% by binder weight), PFW (0–0.3% by volume), and DCWA (0–20% replacement of fine sand). Mechanical performance was assessed through compressive and flexural strength tests. A combined statistical approach using the Pareto chart and ANOVA identified the most influential parameters and their respective contributions to the response variable. The innovative aspect of this research lies in the synergistic integration of MWCNTs, NSP, demolished concrete waste, and polypropylene fiber waste within the mortar matrix, with the incorporation of nanomaterials specifically intended to compensate for the strength reduction typically induced by the use of demolition concrete waste aggregates. Although a potential nano-scale synergy between MWCNTs and NSP was initially considered, the experimental results indicated that the most relevant synergistic effects occurred among broader mix parameters rather than specifically between the two nanomaterials. Even so, when assessed individually, both nanomaterials contributed to improving the mechanical characteristics of the mortar—particularly nanosilica, which demonstrated a more pronounced effect—yet these individual enhancements did not translate into a distinct synergistic interaction between MWCNTs and NSP. The Taguchi DOE proved to be an efficient tool for multiple factor analysis, enabling reliable identification of the most influential parameters with a minimum number of tests. Its application facilitated the development of mortar mixtures that effectively integrate demolition waste while achieving enhanced mechanical performance through nano- and micro-scale reinforcement.

Waste has become an everyday subject, especially its efficient recycling due to the increasing decline in the planet’s primary resources. Therefore, their recovery is intended to be total and with minimal energy consumption. Biomass waste is fully recoverable in raw or processed states and in combination with other compatible waste types (including wastewater from construction, polymers, and sunflower seeds). It represents the basic elements for obtaining synthetic wood to replace natural wood, which is very expensive and difficult to obtain (lasts for several years). This paper proposes three methods to determine the thermal conductivity of these new materials (synthetic wood) to guarantee and optimise their thermal characteristics. The determination of thermal characteristics in insulating materials is usually performed experimentally in a double climate chamber or more simply using a special instrument of the ISOMET type, but under these conditions, the sample must meet certain conditions imposed by the manufacturer to be tested. Thus, two experimental investigation methods are used to which a numerical method is added, which consists of modelling by the finite element method with an adequate programme of heat transfer through these materials. Four samples with variable content of recyclable waste obtained through combinations resulting from six different experimental design plans with two controlled factors were analysed to optimise synthetic wood recipes for the efficiency of their hygro-thermal characteristics. The content of the tested samples varied relative to the quantity and number of recyclable wastes included in the final recipe. Thus, the thermal conductivity obtained was different for each sample but close to that of similar synthetic wood-type materials and natural wood.