Building and Construction Materials

... In the present work ancient Greek, Hellenistic, Roman, Byzantine, post-Byzantine and later historic mortars are sampled from Fortifications, Monasteries, Churches and Historical Buildings in Rhodes, Crete, Corfu, Mount Athos and Constantinople. ...

Curing techniques and curing duration have crucial effects on the strength and other mechanical properties of mortars. Proper curing can protect against moisture loss from fresh mixes. The objective of this experimental work is to examine the compressive strength of ordinary Portland cement mortars (OMs) under various curing regimes and cement fineness. Six different curing methods including water, air, water

Abstract This study investigates the strength reduction associated with incorporating calcium nitrate microcapsules in concrete. It also proposes modifications to the calcium nitrate micro encapsulation procedure to minimize the concrete strength reduction. These modifications consist of altering the continuous phase composition and keeping that of the aqueous phase the same. Amounts of 1%–10% of low Hydrophilic-Lipophilic Balance (HLB) emulsifier and 0.1%–1.0% of oil-soluble sulfonic acid catalyst (by weight of water in the aqueous phase) were dissolved in an organic solvent to prepare the continuous phase. The average diameter and shell thickness of the produced microcapsules were characterized using Scanning Electron Microscopy (SEM). Mortar mixes were prepared for various calcium nitrate concentrations of microcapsules that were encapsulated using the modified procedure. The compressive and flexural strengths and the elastic modulus of the mortar mixes were determined. The results show that the use of the modified encapsulation procedure resulted in a statically insignificant reduction of both compressive and flexural strengths compared to the original encapsulation method. The SEM micrographs of the fracture surface of the samples containing microcapsules showed that the strength reduction may be due to the agglomeration of the un-hydrated particles on the surface (shell) of the microcapsules. The compressive and flexural strengths of samples prepared using the proposed encapsulation procedure were enhanced compared to those prepared using previous encapsulation techniques.

In this paper, the response surface methodology (RSM) and finite element method (FEM) have been used to develop predictive models for the simulation and optimization of heat transfer process. The input variables were the material conductivity as well as the radiation emissivity, length and width of the recesses. The response variable considered was the thermal transmittance. In order to minimize the thermal transmittance, the RSM technique and FEM analyses have been developed in combination and applied to optimize this parameter. A central composite design (CCD) as the standard design of the RSM technique was used to evaluate the effects and interactions of the six previous factors. Next, the optimal design obtained from the RSM analysis is exposed, demonstrating its ability to build a quadratic polynomial model and to solve nonlinear thermal problems. Finally, analysis of variance (ANOVA) has been used to check the significance of response surface polynomials and FEM models so that...

Gypsum plasters, as decorative elements in Mediterranean dwelling buildings, are part of their architectural heritage. Because they were somehow “democratized”, their use was not only rather common but also connected with a certain architectonic style that was vilified a few decades afterwards as too intricate and fatuous.More recently, the public and private entities that own or supervise the buildings in which gypsum plasters were profusely used woke up to the obvious need of rehabilitating these very striking features of the inner rooms and entrances. One such example is the intervention made at the XVIII century Freixo palace in Porto, Portugal.After a brief introduction and characterization of the building, the paper describes the general state of conservation of the gypsum plasters within it, focusing on the following anomalies: water entrance, biological colonisations, salts, chromatic changes, vandalism and abandon, cracking, and incorrect restoration.The works of conservation and rehabilitation of the building are then described in some detail. The most appropriate strategy to tackle the problem is discussed and the actions actually taken (preliminary operations, elimination of biological contaminations, consolidations, stabilization and consolidation of ceilings, removal of incompatible mortars, reinstatement of decorative elements and filling of gaps, cleaning of surfaces, and rehabilitation of paintings) are justified.Some final comments are put forward.

ABSTRACT Foamed geopolymers were synthesised using a South African Class F coal fly ash (FA), sodium hydroxide (NaOH), and the novel foaming agent sodium hypochlorite (NaOCl) at slightly elevated temperatures (90 °C). The synthetic method has the advantage of maintaining control over foaming; the mixed and prepared cementitious slurry containing NaOCl is stable for at least 1 h at room temperature, thus, avoiding premature foaming of the slurry before moulding. In this study, the effect of NaOH/FA on the formation of foamed geopolymers was investigated at predetermined NaOCl/FA ratios (by weight). The NaOH/FA ratio was changed over the range of 0.16–0.24 at a constant NaOCl/FA composition of 0.50. Increasing NaOH/FA improved geopolymerisation up to a ratio of 0.20 and porosity up to a ratio of 0.22, after which geopolymerisation and porosity declined. These results were substantiated through XRD, SEM, FTIR, Raman analyses, mercury intrusion porosimetry, nitrogen adsorption/desorption, and helium density measurements. The formulations developed in this study may be used to fabricate materials suitable for application in construction as light weight fireproof insulation, internal walls or ceiling tiles.

The electrochemical behaviour of reinforcing steel in plain and blended cement concrete specimens placed in sulphate, chloride and sulphate-chloride environments was investigated. The effect of cement composition and the exposure condition on the corrosion behaviour of reinforcing steel was evaluated by measuring corrosion potentials at periodic intervals and conducting potentio-dynamic scans after two and half years of exposure. The corrosion potential data indicated passive corrosion in plain and blended cement concrete specimens placed in the pure sulphate environment. The time to initiation of reinforcement corrosion, however, was higher in blended cements than plain cements in all chloride and chloride-sulphate environments. The concomitant presence of suphate and chloride salts did not significantly influence the time to corrosion initiation. The corrosion rate, however, was significantly influenced by the quantum of sulphate ions associated with the chloride salts. The superior performance of silica fume blended cement, in terms of longer time to corrosion initiation and lower corrosion rate, indicates its potential in enhancing the useful service life of reinforced concrete structures placed in the chloride-sulphate environments.

Abstract The carbon dioxide (CO2), in the presence of water, forms a corrosive medium that reacts with the Portland cement hydrated products in a process denominated carbonation. Carbonation is a topic of great interest for the oil and gas industry due to deleterious and negative effects caused by formations that contain CO2 in their pores to the cements used in cementing operations, as primary and remedial cementing. The corrosive compound present in subsurface can be originated from geological processes, injection techniques for enhanced oil recovery and geological storage. This work evaluated characteristics of CO2 attack in class G Portland cement slurries formulated with different densities: 1890 kg/m3 (15.8 ppg), 1970 kg/m3 (16.5 ppg) and 2030 kg/m3 (17.0 ppg). The slurries were prepared, cured, and subsequently exposed to CO2 during periods of 30, 60 and 90 days in an autoclave with controlled temperature and pressure conditions. After the times inside the autoclave, the samples were analyzed with a pH indicator solution, sedimentation test and scanning electronic microscopy (SEM). The results showed an inversely proportional pattern: the higher the density, the lower the carbonation. The higher content of reactive solids contributed to make the matrix more closed and with a greater availability of hydrated cement products, acting as a barrier to the carbonation advancement.

The paper presents the results of a hydration study performed in order to explain the significant increase in compressive strength at one day of age observed on steam cured mortars when 25% by mass of cement was replaced with a metakaolin. Two CEM I 52.5R cements, differing in reactivity, and a metakaolin (MK) were used. By means of XRD and

Received ZZZ, revised ZZZ, accepted ZZZ Published online ZZZ (Dates will be provided by the publisher.) Keywords end-of-life liquid crystal displays (LCDs), Critical Raw Materials (CRMs), Indium recovery, low cost applications, concrete, Life Cycle Assessment (LCA) According to the WEEE European directives, efforts must be undertaken to reuse or safely dispose LCD waste, however no practical process was reported yet, although it is possible to recover glass, plastic and precious metals, in particular Indium. Indium is one of the element included by the European Commission in the list of 20 raw materials critical for economic importance and high supply risk [1]. The work aims to valorize LCD scraps after Indium recovery with low cost applications both economically and environmentally speaking. Applications have been explored by many researchers, although most focused only on the use of glass powder waste LCD to design concrete. This work deals the use of LCD scraps as it is after cross-current leaching of Indium with H2SO4. The experimental work consists of scraps characterization, washing procedure optimization to remove residual acid, mortar production, performance testing, and LCA. The results show that LCD scraps exhibit little or no pozzolanic activity. This delay on reactivity can be ascribed to organic residues that prevent the pozzolanic reaction and/or to a lower fineness than that typical of binders or fillers. For this reason the actual investigation focuses to exploit the waste as partial replacement of traditional aggregates. Copyright line will be provided by the publisher Copyright line will be provided by the publisher R2 1 Introduction In the near future, a large amount of LCD waste will be generated and this will require the development of procedures for the properly use and safely disposal of those LCD waste, according to the WEEE of the EU[2]. If improperly disposed LCD waste would have significant adverse impacts on human health and the environment. On the other hand it is possible to recover from LCD waste many reusable materials, such as glass, plastic and precious metals, in particular Indium. Indeed Indium is one of the element included by the European Commission in the list of Critical Raw Materials (CRMs) [3] Actually most of the end-of-life LCDs has been treated by incineration or landed. There have been several studies investigating how to recycle LCD panels waste but there has been no practical recycling measure or process reported yet. Most researchers focused on the recovery, of Indium and waste LCD glass, but few are involved in the recycling of polarizing film and none of them considered the possibility of recycling the whole LCD scrap, without the separation of glass and plastic. According to Kae-Long Lin [4], it is possible to separate the polarizing film from the LCD glass by thermal shock and remove the Liquid Crystals through ultrasonic washing after crushing. However, these types of processes needs large energy consumption, such as those required to achieve high temperatures or high pressures. It is therefore important to develop a simpler process, that after the recovery of Indium, enables to valorize the LCD residue scrap with minimal treatments, reducing costs in a eco-friendly way. Use of recycled materials in construction is among the most attractive options because the sector allows the recycling of large quantities. Moreover the construction sites are widespread. In the last few years, many studies have focused on the uses of wasted glass as aggregates for cement concrete or as cement replacements [5]. The finer is the glass powder , the higher is its pozzolanic reactivity. For this reason, Wang [6, 7] replaced a portion of the usual river sand into concrete by sand prepared from discarded LCD glass. The compressive strengths of the concrete with glass sand replacement were higher than the design strengths. The test results indicate that the addition of 20% LCD glass sand to concrete satisfies the slump requirements and improves the strength and durability of concrete. Other analysis have explained the pozzolanic behaviour in cement paste of waste glass from thin film transistor liquid crystal displays. [8]. Accordingly to literature [9] among the waste liquid crystal glasses, the SiO2 rate was the highest, at about 62%, and it can act as a high Si material, followed by Al2O3, Fe2O3, CaO, and K2O. Another study with X-ray fluorescence analysis reported a 64% SiO2 ratio and a 0,3% NaO2 ratio [10]. The chemical composition of the glass is subject to variability but the concentration of SiO2 is still high. The main problem in the use of glass in concrete is that glass is unstable in the