Colloquiam: Durability of Building Materials and Components for Sustainability

Tuning the incompatibility between recycled plastic aggregates and cement matrix with polymer-nano silica hybrids

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:52:36 +0200

Use of recycled waste plastics as the aggregates in construction materials has attracted increasingly gained attention for sustainable construction industry with great environmental benefits. However, the soft plastics and rigid cement matrix can naturally induce the great aggregate-matrix incompatibility, which results in the degradation of engineering properties of cement-based materials containing recycled plastic aggregates (RPAs). To overcome this shortage, this work reports a strategy of tuning the cement matrix with polymer-nano silica (P-nS) hybrids. Ethylene vinyl acetate (EVA) and recycled polypropylene (PP) were selected as the coating polymer and RPA, respectively. Density, strength, water sorptivity and carbonation resistance were measured to assess the physical and mechanical properties of the mortars with recycled PP particles. Microstructure was analyzed using scanning electron microscopy (SEM) with backscattered electron (BSE) and energy-dispersive X-ray spectroscopy (EDS). Results showed that the addition of P-nS hybrids into cement decreases density, mitigates strength reduction, obstructs water sorption, but have positive and negative effects on carbonation resistance of the cement mortars with RPA. The P-nS hybrids build the organic–organic links between the cement matrix and RPA, and coordinate their deformations. The findings of this work proof the proposed strategy of tuning the compatibility between soft aggregates and rigid matrix with the engineered microstructure towards enhancing the recyclability of waste plastics in construction materials.

Recycling of Polypropylene Fibre Reinforced Concrete: Use of Recycled Aggregate and Recovered Fibre in New Concrete

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:51:36 +0200

The study aims at investigating the feasibility of using recycled aggregate (RA) and recovered fibres (RF) obtained from recycling of polypropylene fibre reinforced concrete (PPFRC) in new concrete production. The mechanical properties were compared between a parent concrete, polypropylene fibre reinforced recycled aggregate concrete (PPRAC), and recovered polypropylene fibre concrete (Re-PPRFC). All concretes were designed to have the same compressive strength and slump. The parent concrete was produced with 9 kg/m3 of polypropylene fibre. After recycling, the RA and RF were collected and new concretes with RA and RF, PPRAC and PPRFC, respectively, were produced with the same fibre content as the parent concretes. The strain-stress relationship in compression and residual tensile strength were tested. The results obtained for PPFRC, PPRAC and rePPRFC were compared. The results show that the RA and RF obtained by PPFRC recycling can benefit new concrete production.

Numerical Simulation on the Influences of Wind Pressure on Jet Characteristics of Shotcrete

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:50:37 +0200

A gas-liquid two phases model of shotcrete was developed to simulate the whole process from the spouting of concrete from nozzle, the scattering in the flow field to its colliding with a wall based on computational fluid dynamics theory, in which concrete was regarded as a Bingham fluid. The influences of wind pressures、 pumping speeds、 air incident angles and rheological parameters on five characteristic parameters including spouting velocity, jet velocity, jet trajectory, collision velocity and distribution of shotcrete on the wall were analyzed in depth. Results showed that concrete was gradually mixed well with air in the nozzle with an increasing average velocity, and the increase of velocity was most pronounced in the contraction section of nozzle. With the increases of wind pressures and pumping speeds, the spouting velocity and spouting mass of concrete both increased. Higher wind pressure and pumping speed led to larger jet velocity and more concentrated distribution, resulting in significantly longer jet distance, higher collision velocity and larger distribution area. The collision velocity and volume fraction of concrete on the wall were distributed symmetrically along Y axis, shifting towards the direction of gravity. With the increases of air incident angles, the spouting velocity and spouting mass of concrete both decreased, the shifting to gravity is weakened and the volume fraction decreased first and then increased. When plastic viscosity decreased, the spouting velocity and spouting mass of concrete both increased, accompanying with a higher jet velocity, a longer spraying distance and a larger distribution area.

Effect of Pre-calcination of Lead-zinc Tailings on the Activation of Blast Furnace Slag

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:49:36 +0200

Blast furnace slag and lead-zinc tailings (LZTs) are solid wastes from the iron-making and mining industries, respectively. In order to reuse these solid wastes, the LZTs were pre-calcined at different temperatures and then explored whether it is capable of being the activator of slag. The effects of pre-calcination on the phase composition of LZTs were elucidated by XRD. The compressive strength of LZTs-activated slag pastes was investigated, and the mineral composition and microstructure of the pastes were detected by XRD and SEM. The results imply that with the elevating of heating temperature from 500 ℃ to 1000 ℃, the dolomite in LZTs decompose into CaO and MgO, and the oxidation of pyrite resulted in the formation of Fe2O3 and gaseous SO3, then SO3 reacted with a part of formed CaO to produce CaSO4. The resulting CaSO4 and CaO can become the sulfate activator and alkaline activator of slag, respectively. The LZTs-activated slag pastes prepared with the LZTs preheated at 800 ℃ exhibit the highest strength at 90 d, which yield 24 MPa. The hydration products of LZTs-activated slag were ettringite and calcium silicate hydrates (C-S-H gel). Large amounts of dense C-S-H gel bond together, connecting most of the ettringite networks into a whole, thus forming a dense structure and effectively improving the strength of LZTs-activated slag. The outcome of this study provides a potential disposing or reusing approach of the large amounts of LZTs.

Probability Durability Assessment of Existing Concrete Structures in Carbonation Environment

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:48:36 +0200

In a particular service environment, the calculation models used to determine the durability of existing concrete structures differ from those employed in the design phase. This paper presents a methodology for assessing the probability durability of existing structures, taking into account the nondestructive testing results and the target reliability index. The initial step involves introducing a correction coefficient into the carbonation and corrosion development theory model. This coefficient is necessary to account for the correction associated with the corrosion monitoring of steel. The values of this coefficient should be determined based on the actual testing results, specifically considering the presence of reinforcing steel corrosion. Next, a probability expression is proposed using the measured results of probability characteristics and the target reliability index. This approach takes inspiration from the design-value method and the existing theory of structure reliability. It also takes into account the specific variables of concrete protective cover thickness and the compressive strength as the fundamental random variables. The residual working life can be calculated as the outcome of a durability assessment through quantitative analysis. This calculation can serve as a valuable reference for the maintenance program.

Overview on Testing Method of Internal Damage to Special-shaped Stone Components in Palace Museum

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:47:37 +0200

Irregular historic stone components are very important parts of the ancient architecture in the Palace Museum. They have been subjected to deteriorations from surface to interior under the combined effects of many factors such as wetting and drying, salt dissolution and recrystallization, selfload, external load, and environment action. The internal damages in these stone components are difficult to detect but are crucial for the assessment of the intact of these components. In order to detect the internal damage of stone components, especially the special-shaped stone components, which cannot be tested by comment methods. Taking evaluation on preservation status of stone components in a qualitative and quantitative way， with application of ultrasonic computerized tomography and regular inspection, a convenient, safe, economical, efficient, and readable method for detecting the internal damage of irregular stone components can be established in order to detect any safety hazards as early as possible and provide data support for assessment and conservation, achieving a better preventive conservation.

Evaluating the Future Moisture Performance of the Stucco-Clad Wall Assembly in Selected Canadian Cities

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:46:37 +0200

Due to climate change, it is expected that the amount of precipitation in most parts of Canada will increase in the coming decades. Consequently, the building envelope exposed to such climate could experience a higher moisture load than in the past, which could have a negative impact on its performance in the long run. The stucco-clad wall assembly, which has been widely employed in the construction of low-rise residential buildings throughout Canada may not be adequately designed to be resilient to the future climate. Thus, in the study described in this paper, the future moisture performance of the stucco-clad wall assembly located in two Canadian cities with different levels of moisture load, i.e., Vancouver and Calgary, subjected to projected future climate is investigated. The analysis includes two phases: conducting watertightness for a full-scale stucco wall specimen to determine the relationship between the climate data and the moisture load in the wall assembly and implementing hygrothermal simulations using the relationship obtained from the watertightness test for the performance assessment. Mould growth index at the exterior surface of the oriented strand board of stucco-clad wall assembly for the historical and projected future time periods is compared and discussed.

Analysis of Thermal Bridges in Concrete and Cross-Laminated Timber (CLT) Constructions: A Numerical Study

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:45:35 +0200

The thermal efficiency of a building envelope relies on various factors, including insulation resistance, continuity, the thermal conductivity of structural materials, and the presence of thermal bridges. This study focuses on studying the thermal performance of thermal bridge details in two construction types: concrete and Concrete and Cross-Laminated Timber (CLT). For the study, two common building envelope details with significant thermal bridges are considered, balcony and intermediate wall-to-floor connections. Utilizing the finite element program COMSOL Multiphysics, hourly transient simulations were conducted over a one-year period to assess the heat loss/gain associated with thermal bridges, considering daily, seasonal, and annual heat flow for two diverse climatic conditions (hot weather Houston-Climate Zone 2 and cold weather Toronto-Climate Zone 6). The findings demonstrate that thermal bridges constructed from CLT outperformed those made of concrete. In Toronto, the annual heat flow for the concrete balcony was 146% higher compared to CLT, while in Houston, it was 67% higher. However, this trend was significantly reduced for the wall-to-floor detail, with a concrete detail showing a 13% increase in heat flow for Toronto and a 7% decrease in annual heat flow for Houston. Furthermore, the dynamic analysis revealed notable heat flow magnitude changes in the balcony detail, highlighting the importance of thermal conductivity, while the wall-to-floor detail exhibited dampening fluctuations in heat flow, emphasizing the material's heat capacity importance in this context.

Use of Machine Learning in Processes Optimization for Drinking Water Treatment Plant Butoniga (Istria, Croatia)

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:44:38 +0200

Drinking water treatment plant Butoniga is located in central Istria (Croatia) downstream of the Butoniga reservoir. The Butoniga reservoir is an artificial lake created in 1987 with two main objectives: 1) protection from adverse water impacts, and 2) drinking water supply. The operation of the drinking water treatment plant is mainly related to the tourist season, and the 5.000.000 m3 of produced and distributed drinking water annually, 3.000.000 m3 is produced and distributed during June 15 to September 15, when the raw water quality in the Butoniga reservoir is the worst. Regarding this, main problem with Butoniga reservoir and thus drinking water treatment plant appear in summer months when water temperature is the most critical parameter and raw water for the treatment process must be captured from the lowest layer of the reservoir which have increased concentrations of Mn, Fe, NH4 and lower pH values and thus influence on the treatment processes. To deal with this problem, model predicting Mn, seven days in advance is build using machine learning approaches. Build model have high accuracy compared to the measured data, with a good prediction of the peak values. As such, obtained model can help in optimization of the treatment processes which are depending on the quality of raw water, and overall, in sustainability and management of the drinking water treatment plant Butoniga.

Proposal of Soundness Index for Existing RC Apartment Building for Proper Management Through Visual Monitoring

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:43:40 +0200

A numerical index for housing complexes of reinforced concrete maintained properly was proposed. First, based on the literature review, deterioration grade and a method for evaluating soundness for RC housing complexes, which determined by visual inspection, was proposed. And then, accelerated deterioration experiments of small RC wall and investigation of existing buildings were conducted. From the study, a correlation between the deterioration grade determined visually and rebar corrosion grade was confirmed. By using building health H(t), that is proposed as index of soundness for existing RC housing complexes, RC housing complexes whose age were 46 to 69 years were evaluated. From the study, it was confirmed how much deterioration the evaluation value indicates.

Effect of Moderately Elevated Temperatures on Performance of Portland Cement Concrete

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:42:37 +0200

High temperature is one of the critical factors leading to the change in concrete performance since it affects the physical structure and chemical components of concrete. However, some concrete structures are continuously subjected to moderately elevated temperatures (typically less than 200 ℃) when operating, such as chimneys for the metallurgical industry and structures in nuclear power plants. The deterioration process of these structures could be caused and accelerated by a high-temperature environment. Thus, the safety and performance of these concrete structures at elevated temperatures during service life are crucial. This paper aims to investigate the change in concrete performance exposed to sustained moderately high temperatures. The concrete cured for 56 days was subjected to temperatures ranging from 65℃ to 200 ℃ for 28 days. The mechanical properties of concrete at different heating temperatures were tested, including compressive strength, splitting tensile strength and modulus of elasticity. Meanwhile, concrete’s durability after heating was evaluated using the concrete electrical resistivity test. The concrete elevated-temperature performance was compared to identical concretes at room temperatures, and the evolution of each property was analyzed. Based on experimental results, the long-term performance of concrete in a moderately elevated temperature environment is predicted.

Heavy Metals Immobilization Property and Mechanisms of LDHs-modified Cementitious Materials

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:41:36 +0200

Layered double hydroxide (LDH) has a positive effect on the adsorption and immobilization of heavy metals. The compressive strength and the heavy metal ions Pb2+ immobilization of CaAl-LDH modified cement paste were studied in this paper. Through research, it was found that compared with the cement paste sample with a Pb2+ content of 1% after curing for 7d and 28d, the addition of CaAlLDH to the cement paste sample increased the compressive strength by 6.1% and 1.6%, respectively, demonstrating the enhancing effect of CaAl-LDH on the strength of cement paste. Compared with the sample containing only Pb2+, the addition of CaAl-LDH to the cement increased the immobilization rate by 0.3% after 12 hours of leaching time and showed varying degrees of improvement at different leaching times. The immobilization mechanism of heavy metals in LDH blended cement paste was revealed by microstructure characterization. It was founded that Pb2+ can replace Ca2+ in AFt, AFm, and LDH, and can co-precipitate with OH-.

Chemo-physical Analysis on Corrosion Initiation of Offshore Structures under Chloride Attack

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:40:36 +0200

Chloride ingress has been recognized as a main factor inducing the corrosion of offshore reinforced concrete structures. It is acknowledged that the chemical attack can lead to concrete property deterioration, which inevitably affects the reinforcement corrosion. Herein, the influence of the concrete aging on the chloride-induced corrosion initiation is systematically evaluated by a novel numerical framework. In this framework, the chemo-physical analysis is conducted based on coupled NernstPlanck model and Gibbs energy minimization model. The proposed method is first validated against reported experimental results. It is found that the chloride ingress is always accompanied by leaching of hydrates near the exposure surface, leading to the porosity enlargement. Moreover, due to chemical binding of chloride to monosulfoaluminate, ettringite continuously precipitates under the function of released sulfate ions. Through a series of numerical analyses, it is revealed that the newly formed hydrates impose competitive effects on chloride transportation due to the simultaneous pore-clogging and expansion-induced microcracks. Chloride-induced corrosion occurs earlier in the situation that the effect of microcracks overcomes that of pore clogging, otherwise, the corrosion is delayed.

Carbonation-induced Early Corrosion Propagation Based Service Life Assessment Model (CECP-SAM)

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:39:35 +0200

Supplementary cementitious materials (SCMs) are widely used for sustainable concrete. However, this is challenged due to the deteriorated resistance towards carbonation-induced corrosion. This paper introduces the establishment of a novel carbonation-induced early corrosion propagation based service life assessment model (CECP-SAM). This model is characterized by considering the early corrosion propagation (incipient cracking) and the use of supplementary cementitious materials. Based on experimental and numerical methods, the effects of binders, water/binder (W/B) ratio, exposure condition, cover thickness, rebar diameter, semi-carbonation zone, cathode-anode ratio on service life are investigated by CECP-SAM. The model is justified by using the results from a field investigation in Hong Kong. Performance-based service life equations are also given based on CECP-SAM.

Service Life Prediction of Concrete Against Freezing and Thawing Based on Water Absorption Results

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:38:38 +0200

Freezing and thawing resistance performance of concrete is a critical issue when evaluating the durability performance of concrete. This paper aims to predict the freezing and thawing resistance performance of concrete based water absorption indexes, meanwhile, five groups of experiments on porosity, short-term water absorption, long-term water absorption, MIP and pore structure scanning were respectively carried out for concrete. According to the experimental results, the important indexes such as porosity, water absorption, gas content and bubble spacing coefficient were obtained, which provided the basis for the prediction of durability and service life. The concept of equilibrium time ratio is introduced to simplify the calculation process. Based on the critical saturation theory, the service life of concrete against freezing and thawing is predicted by combining the environmental parameters and the indexes measured in experiments. The calculated results verified that the freeze-thaw durability life of air-entrained concrete is significantly increased compared with that of concrete without air-entrained concrete. In addition, a wide range of the service life was predicted for the 5 mixes, and the results could provide a guidance for selecting a proper mix design of concrete subjected to freezing and thawing.

Microstructure of Cement Paste with Expansive Additives under Free and Restrained Conditions

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:37:37 +0200

Expansive additives (EAs) have been widely used to reduce the risk of cracking due to shrinkage. Such additives cause early age expansion of concrete due to the formation of Portlandite and Ettringite in the pores of the cement paste, which affects the cement paste's microstructure. The presence of external restraints in the form of reinforcement and support affects the expansion and, ultimately the microstructure of cement paste. In the current study, the microstructure of cement paste with expansive additives is studied using mercury intrusion porosimetry (MIP). A free lime-based EA, with 10 and 15% (by weight) cement replacement ratios, is studied in the current study. The porosity and pore size distribution of the cement paste with EA were studied under free and restrained conditions. Results show that the under the stress-free condition, the porosity of the paste increased, while under the restrained condition, the porosity remained much similar to the reference case of OPC. Further, the pore size distribution of the cement paste with EA under free and restrained conditions is explained, and the effect of EA and restraint on the microstructure is discussed.

Study on Release Performance of Concrete Release Agent

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:36:38 +0200

In this paper, the effects of types of concrete release agent, the amount of brushing per unitarea and the 1d's strength of concrete on the release performance were studied. The adhesion and filmforming ability of O/W emulsion release agent was improved by adding high polymer. The results showthat the 1d's strength of concrete has no effect on the release performance of the release agent. The mostimportant factors affecting the release performance are brushing amount per unit area and the type ofrelease agent. O/W emulsion release agent with polyacrylamide and polyethylene glycol all stick mold. The more they are added, the heavier the stickiness is. While, the release performance with polyethyleneglycol is very close to blank sample.

Properties of Mineral Powders Modified Foamed Concrete

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:35:35 +0200

In order to improve the stability of lightweight foamed concrete, the particle-stabilized foam (PSF) has been proposed because of its high stability. However, most PSFs added particles to foams, and few researchers have investigated whether the stabilization effect exists when particles are added to the paste. In this study, a new type of foamed concrete was prepared by adding different kinds of mineral powders to cement and using ionic surfactants to prepare foam. The influence of different mineral powders on the mechanical properties and durability of foamed concrete was investigated. Results showed that mineral powders decreased the drainage and disproportionation of foam, which stabilizes the foam. The excellent stability is attributed to the interaction between the mineral powders and ionic surfactants, which allows the mineral powders to adhere to the foam surface and form a dense granular film layer. Moreover, due to the interaction between mineral powders and ionic surfactants, hardened foamed concrete has a robust pore structure, which improves its properties.

Influence of Alkali-resistant Glass Fibers Distribution on Properties of Cementitious Composites

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:34:38 +0200

The waste hierarchy establishes a prioritized framework for effective waste management, where higher levels such as prevention, re-use, and recovery are associated with the conservation of primary resources and the retrieval of secondary resources. This approach aligns with the objectives of the construction industry, which aims to promote the efficient utilization of resources by treating raw materials in an environmentally responsible manner. In this context, utilizing waste fibers to reinforce cementitious composites becomes more logical than producing new fibers with similar properties. These waste fibers typically originate from the production of high-performance technical textiles used for structural repair and rehabilitation. By reusing these waste materials, the construction industry contributes a circular economy in its own sector and fosters cross-sectoral industrial symbiosis. Although the potential benefits and positive environmental impact of utilizing such materials are recognized, their influence on the properties of composites requires further investigation. This study examines the impact of production waste glass fibers on the properties of the mortar in both the fresh and hardened states. The study focusses on properties such as compressive strength and toughness. To gain a better understanding of the fibers’ contribution to the matrix properties, an investigation was conducted using µCT. The study focuses on investigating the effects of waste fibers with lengths of 5 and 10 mm and different dosages (0.2, 0.6 vol.%) on the properties of high-strength mortar, comparing them with factory fibers.

Study on Natural Passivation Behavior of Corrosion-resistant Steel Rebars in the Mortar

Jesús Sánchez Pinedo — Tue, 03 Oct 2023 12:33:35 +0200

The passivation behavior of HRB400 carbon steel rebar, 304 austenitic stainless steel rebar and 2304 austenitic-ferritic duplex stainless steel rebar during curing stage of mortar was studied by electrochemical testing techniques such as open-circuit potential, electrochemical impedance spectroscopy and linear polarization curve, and the corrosion resistance of the passivation film of the three rebars was compared to provide a reference for the practical engineering application of corrosion-resistant steel rebars. The study shows that all three types of steel rebars can be passivated during the 28 days curing stage of mortar, and 2304 duplex stainless steel rebars have the best passivation film corrosion resistance, followed by 304 stainless steel rebars, and HRB400 steel rebar was the worst.