Linear Drying Shrinkage Research Articles

Synergistic impact of geopolymer binder and recycled coarse aggregates on the performance of concrete masonry units

This study examines the combined effect of geopolymeric binder and recycled coarse aggregates (RCA) on the properties of concrete masonry units (CMU). A target 1-day compressive strength of at least 13.8 MPa was attained for all mixes to satisfy the load-bearing strength requirements. Geopolymer mixes made with RCA at replacement rates of up to 100 % were evaluated and compared to a cementitious control mix made with natural coarse aggregates. The environmental and economic impacts were then integrated with the quantity of waste valorized and compressive strength in a multifunctional performance index. Experimental results showed that the utilization of geopolymers as a substitute for Portland cement in the production of CMU did not impact the oven-dry density but reduced the water absorption capacity by up to 26 %. Although the incorporation of RCA negatively impacted these two properties, their values remained within the acceptable range stated by the standards. The geopolymer CMU mix made without RCA had 9 and 25 % lower 28-day compressive and splitting tensile strengths compared to the cement control mix, respectively. Subsequent RCA replacement further reduced these mechanical properties. While the linear drying shrinkage was reduced upon substituting the cementitious binder with the geopolymeric counterpart, RCA replacement of up to 100 % increased the linear drying shrinkage to reach 0.091 %, exceeding the limit set by the standard. Overall, the CMU mix made with geopolymer binder and 75–100 % RCA was found to be optimal for load-bearing applications.

Development of bio-based lightweight and thermally insulated bricks: Efficient energy performance, thermal comfort, and CO2 emission of residential buildings in hot arid climates

This study explores the viability of using industrial wastewater sludge (IWWS), generated by the mycelium treatment of dyeing wastewater, for the fabrication of lightweight and thermally insulating bricks. The pulverized IWWS was used at various replacement ratios of 0, 5, 10, 15, and 20 wt% of clay. The mixture was subjected to firing temperatures of 700, 800, and 900 °C. The effect of applying IWWS to the brick characteristics is assessed through an examination of the physico-mechanical and thermal properties. The utilization of IWWS resulted in a significant enhancement in apparent porosity (34.4 %), cold water absorption (25.6 %), boiling water absorption (28.5 %), linear drying shrinkage (5.1 %), and linear firing shrinkage (7.9 %) using 20 % IWWS at 900 °C. Furthermore, the density, compressive strength, and thermal conductivity were reduced as the substitution IWWS ratio increased, reaching up to 1662.9 kg/m3, 11.56 MPa, and 0.198 W/m.K., respectively, using 20 wt% IWWS at 900 °C. The effect of fabricated fired bricks (FBs) on the thermal insulation, CO2 emissions, and energy consumption of residential buildings was tested. This is accomplished by using energy modeling tools, such as Honeybee, Ladybug, and Climate Studio (Grasshopper plugins), in addition to Galapagos for optimizing wall design. The suggested wall design is being used in a communal residential building located in two distinct climatic regions, namely Cairo in Egypt and Jazan in Saudi Arabia. According to the projected mean vote (PMV) and anticipated percentage of discontent (PPD) measures, the utilization of fabricated FBs as wall materials exhibits significant improvements in thermal comfort. Furthermore, they lead to a 6 % and 7 % drop in CO2 emissions in Cairo and Jazan cities, respectively, as well as a significant 38.8 % and 39 % reduction in energy consumption in Cairo and Jazan cities, respectively. Therefore, the use of fabricated FBs demonstrates itself as a feasible and environmentally friendly choice for building construction.

Experimental Study on Mechanical Properties and Drying Shrinkage Compensation of Solidified Ultra-Fine Dredged Sand Blocks Made with GGBS-Based Geopolymer

As natural aggregates become increasingly scarce, attention has turned to ultra-fine dredged sand (UDS) generated in waterway regulation engineering. UDS is typically challenging to utilize due to its high clay content and high water demand. This article uses ground granulated blast-furnace slag (GGBS)-based geopolymer to solidify UDS, along with sodium silicate (SS) and sodium hydroxide (SH) as alkaline activators. This paper explores the effects of SS modulus (SiO2/Na2O molar ratio) and mass percentage content of Na2O on the fluidity, setting time, mechanical properties, and shrinkage behavior of hybrid UDS-GGBS geopolymer (HUGG) paste. According to the research findings, increased SS modulus and Na2O content lead to decreased fluidity and setting time. When the Na2O content reaches 6%, flash coagulation occurs in the slurry, leading to more internal shrinkage cracks and pores. This has been confirmed by scanning electron microscope (SEM) analysis. When Na2O content is 5%, and SS modulus is 1.0, the 90-day maximum compressive strength reaches 56.53 MPa, corresponding to a splitting tensile strength of 6.83 MPa, which can be considered the optimal formulation. Meanwhile, basalt and polypropylene fibers (BF and PPF) are chosen to compensate for the susceptibility to drying shrinkage. Both BF and PPF can significantly inhibit the linear drying shrinkage of the HUGG paste. The BF’s ability to enhance mechanical properties is more robust than PPF’s, which can make the paste more homogeneous. The research contributes an effective method for the resource utilization of UDS.

Fabrication of Thermal Insulation Bricks Using Pleurotus florida Spent Mushroom.

This study explores the potential for making lightweight bricks via the use of dry, pulverized spent mushroom materials (SMM) as a thermal insulator. There are five distinct replacement proportions of SMM that are used, and they range from 0% to 15% of the weight of the clay. The firing of the fabricated bricks at temperatures of 700, 800, and 900 °C led to the development of pores on the interior surface of the bricks as a consequence of the decomposition of SMM. The impact of SMM on the physicomechanical characteristics of fabricated bricks is assessed based on standard codes. Compressive strength, bulk density, and thermal conductivity decreased as the SMM content increased, reaching up to 8.7 MPa, 1420 kg/m3, and 0.29 W/mK at 900 °C and 15% substitution percentage. However, cold water absorption, boiling water absorption, linear drying shrinkage, linear firing shrinkage, and apparent porosity increased with the increase in SMM, reaching 23.6%, 25.3%, and 36.6% at 900 °C and 15% substitution percentage. In the study simulation model, there was a significant improvement in energy consumption, which reached an overall reduction of 29.23% and 21.49% in Cario and Jazan cities, respectively.

Effect of agricultural biomass wastes on thermal insulation and self-cleaning of fired bricks

This research investigates the feasibility of using dry crushed pomegranate peel waste as thermal insulator to produce light clay bricks. Pomegranate peel waste (PW) is used with different substitution levels of 0%, 5%, 7.5%, 10% and 15% of clay weight. The clay bricks were heated at temperatures of 700, 800, and 900 °C, that resulted in the formation of internal pores due to the combustion of PW. The bulk density, water absorption, porosity, shrinkage, and compressive strength are examined to evaluate the effect of using PW on the physical and mechanical properties of thermal insulation bricks. Also, the investigation of the effect of photocatalytic activity of bricks under sunlight irradiation is carried out. The use of PW increased the thermal conductivity up to 21% at 900 °C, water absorption from 22.6% in cold water to 29.1% in boiling water, density from 2.5% at 800 °C to 7.6% at 900 °C, and shrinkage from 4.3% in linear drying shrinkage to 5.4% in linear firing shrinkage. The heated brick samples at 700 °C showed greater photodegradation efficiency than firing clay at 800 °C and 900 °C. Moreover, the compressive strength decreased with the increase in replacement rate, reaching up to 74% for 15 wt% PW. This study confirms that lightweight heated bricks with low thermal conductivity and a reasonable compressive strength can be made using PW as a pore-forming agent.

Prediction of physical-mechanical properties of hollow interlocking compressed unstabilized and stabilized earth blocks at different moisture conditions using ultrasonic pulse velocity

This paper aims to investigate the effectiveness of ultrasonic pulse velocity (UPV) method to evaluate the physical-mechanical properties of hollow interlocking compressed unstabilized and stabilized earth blocks (ICSEBs) at different moisture conditions. The objective is to establish correlations between destructive and non-destructive tests. To this end, unstabilized and cement (4%, 6%, 8% and 10% by weight) stabilized blocks were prepared and characterized for density, porosity, linear drying shrinkage and water absorption, compressive strength, flexural and splitting tensile strength, and UPV at 28 days in air-dry, oven dry and wet states. Additionally, X-ray diffraction and scanning electron microscopy (SEM) tests were performed to identify the effect of cement content on microstructure and phase composition. The relationships among physical-mechanical parameters and UPV were evaluated. Finally, a statistical regression analysis was conducted, and empirical equations are proposed to predict the mechanical resistance of ICSEB in terms of moisture content, cement content, dry density and UPV. Results indicate that both moisture content and cement content have a significant effect on physical-mechanical properties and UPV of ICSEBs. The compressive strength, flexural and splitting tensile strength, porosity of ICSEBs reduces with an increase in moisture content while density increases for all cement contents. However, the addition of cement significantly improved the block properties. As the cement content increases from 4 to 10% the compressive strength, flexural and tensile strength increase by about 3.7, 5.4 and 6.5 times in air-dry state, respectively. It was observed that mechanical response of blocks is more sensitive to water content than cement content. Cement content ≥ 6% is recommended for production of durable ICSEB. Microstructural investigation confirmed that addition of cement content reduces the pores and densifies the microstructure. In unstabilized blocks, UPV reduces with an increase in moisture content; whereas in stabilized blocks higher UPV is obtained in air-dry state followed by wet and oven-dry states. A strong correlation exists between UPV and physical-mechanical properties. The proposed equations obtained from statistical analysis are capable of predicting the compressive strength, flexural and splitting tensile strength with fair accuracy. These findings confirm that UPV can be effectively used for assessing the performance of ICSEBs.

Earth Plasters: The Influence of Clay Mineralogy in the Plasters’ Properties

ABSTRACT Earth-based mortars have been used all over the world since ancient times in an extensive range of building types from vernacular architecture to monuments. Plastering is one of the most common contemporary applications of earth-based mortars used for earthen-building conservation or modern architecture. Raw earth is a very diverse natural material, and clay minerals play a key role in plaster properties being responsible for their setting process and providing the capacity of balancing the indoor hygrometric conditions of buildings. This capacity offers significant benefits to energy savings delivering comfort and health of inhabitants and also contributes to building conservation. For this study, three mortars were produced with different clayish earths to assess the influence of clay mineralogy. Mortars characterization confirmed that clay mineralogy drives important plaster properties, such as vapour adsorption and drying shrinkage, while also having a significant influence on mechanical strength, dry abrasion, and thermal conductivity. Within the studied mortars, illitic clayish earth stands outs as more adequate for earth-based plasters, showing balanced properties, namely linear drying shrinkage, mechanical strength, dry abrasion, and water vapour adsorption.

Determination and adjustment of drying parameters of Tunisian ceramic bodies

This work deals with the mineralogical, physico-chemical and geotechnical analyses of representative Aptian clays in the north-east of Tunisia. X-ray diffraction reveals a predominance of illite (50–60 wt%) associated with kaolinite and interstratified illite/smectite. The accessory minerals detected in raw materials are quartz, calcite and Na–feldspar. The average amounts of silica, alumina and alkalis are 52, 20 and 3.5 wt%, respectively. The contents of lime and iron vary between 4 and 8 wt %. The plasticity test shows medium values of plasticity index (16–28 wt%). The linear drying shrinkage is weak (less than 0.99 wt%) which makes these clays suitable for fast drying. The firing shrinkage and expansion are limited. A lower firing and drying temperature allow significant energy savings. Currently, these clays are used in the industry for manufacturing earthenware tiles. For the optimum exploitation of the clay materials and improvement of production conditions, a mathematical formulationis established for the drying parameters. These models predict drying shrinkage (d), bending strength after drying (b) and residual moisture (r) from initial moisture (m) and pressing pressure (p).

Fabrication, microstructure and properties of bricks fired from lake sediment, cinder and sewage sludge

Lake sediment, cinder and sewage sludge were used as raw materials to prepare three types of fired brick samples. Measurements were made on the plasticity index, oxide composition and mineral composition of raw materials and the linear drying shrinkage, water absorption, bulk density, compressive strength, thermal conductivity and freeze-thaw resistance of the fired brick samples were investigated. XRD, SEM and MIP were used to analyze the phase composition and microstructure of bricks. It was found that sewage sludge can be used together with lake sediment and cinder to produce bricks which meet the requirements of Chinese specifications. The incorporation of cinder and sewage sludge into lake sediment reduced the linear drying shrinkage of adobe, but at the same time increased the water adsorption and lowered the compressive strength and the frost resistance of the fired brick. The difference in the properties of the three types of bricks can be explained from the characteristics of their microstructure.

Egyptian Smectite-Rich Clays for Lightweight and Heavy Clay Products

Suitability of three technological samples representing smectite-rich clay deposits of El-Minya, Egypt for lightweight and heavy clay products was studied. According to particle-size, mineral, and chemical composition of the clay samples, one sample was rejected due to its high content of sulphate gypsum and anhydrite minerals. Ceramic properties before firing of a sample representing the other two clays with and without addition of 40% sand grains were studied. These include rate of slaking in water and water of plasticity as well as linear drying shrinkage and drying sensitivity coefficient (DSC). The representative clay sample without addition of sand grains was assessed for lightweight bloated clay aggregate by processing its plastic pellets up to firing at 1000-1300 o C. Also, suitability of shaped plastic clay-sand bodies for heavy clay products was studied after firing up to 800-1200 o C by following their densification parameters in terms of total linear shrinkage (TLS), bulk density (BD), water absorption (WA), and crushing strength (CS). Efflorescence test was also conducted to follow up deposition of any white water-soluble sulphate salts on surfaces of the wet fired bodies after drying. The three samples of El-Minya clays contain major clay particles and lesser silt and sand particles due mainly to its high content of smectite with lesser kaolinite and illite clay minerals. In addition, variable quartz, feldspar, and hematite as well as gypsum and anhydrite non-clay minerals are detected and one of these samples was rejected due to its high content of the latter minerals. The representative sample of the other two clays is of a low-grade due mainly to its low-alumina as well as high silica and fluxing oxide contents. When 40% of sand grains was added to the clay sample, water of plasticity is decreased from ~51 to 25% and LDS as well as DSC were reduced from 13.3 to 8.1% and from 1.4 to 0.92, respectively. Furthermore, the shaped 60/40 clay/sand bodies were partially and fully vitrified after firing for 2 hours up to 1000 and 1200 o C, respectively. The partial and fully vitrified bodies show accepted WA, TLS, BD and CS levels, according to the Egyptian and International standards for building bricks and ceramic tiles, respectively. The fired bodies were also classified as not-effloresced types after testing for efflorescence. In addition, the clay sample was also processed as lightweight bloated clay aggregate with grain density of 0.7-0.8 g/cm 3 after firing up to 1300 o C. This is mainly attributed to developing of sufficient amount of a silicate liquid phase viscous enough to entrap the oxygen gas, simultaneously evolved due to partial reduction of Fe 2 O 3 of the clay into FeO with the formation of magnetite (Fe 3 O 4 ) spinel.

Performance evaluation of structural concrete using controlled quality coarse and fine recycled concrete aggregate

This paper presents the fresh, mechanical, and durability performance, of a structural concrete mix classified as C-1, by the Canadian Standards Association (CSA) made with controlled quality Recycled Concrete Aggregate (RCA). Five mixes with water-to-cementing material (w/cm) ratio of 0.40 were produced with various RCA contents and tested against two 0% RCA control mixes made with General Use (GU) cement, and General Use Limestone cement (GUL). The RCA contents in the mixes were 10%, 20%, and 30% by coarse aggregate volume replacement, as well as 10% and 20% fine and coarse (granular) aggregate volume replacement. All evaluated mixes met the specifications from the CSA for fresh, mechanical, and durability properties. The coarse RCA mixes performed better than the granular RCA mixes in terms of flexural and splitting tensile strengths, linear drying shrinkage, water sorptivity, and rapid chloride-ion permeability, where the test results were significantly affected by the ultra fines present in the granular RCA.

Influence of sand on the mechanical properties of metakaolin geopolymers

Metakaolin geopolymers require a high water content to have appropriate rheology for use in some applications and these mixes exhibit extensive drying shrinkage and cracking. This work aimed to understand the effect of adding sand as inert filler to metakaolin geopolymers. It is found that the viscosity increases with sand addition and mortars become unworkable when more than 40vol% sand is added. Linear drying shrinkage was reduced from about 8% in the absence of sand to less than 1% with 38vol% sand addition. Moreover, geopolymer mortars containing more than 15vol% sand can withstand drying at 110°C without cracking. Because sand addition to metakaolin geopolymer mortars increases viscosity less than a reduction in water content it is possible to formulate mortars that flow but do not crack on drying and these materials have potential for use in a range of architectural and restoration applications.

Geopolymer prepared with high-magnesium nickel slag: Characterization of properties and microstructure

High-magnesium nickel slag (HMNS) is a hazardous waste that is generated in nickel pyrometallurgical production. The present work investigates the feasibility of using this slag in geopolymer manufacturing. The effects of HMNS addition on the reaction, mechanical properties and microstructure of fly ash-based geopolymers are studied through isothermal conduction calorimetry (ICC), compressive strength testing, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), X-ray diffractometry (XRD) and drying shrinkage testing. The results showed that the major phase in fly ash-HMNS geopolymers was a type of sodium magnesium aluminosilicate gel (N–M–A–S) with amorphous features. The Si/Al ratio of the gel phase increased with HMNS content due to the high silica supplied by HMNS. In terms of compressive strength, the maximal strength of fly ash-based geopolymers was achieved by 20% HMNS substitution. At this optimal content, the sample possessed a refiner pore structure and lower linear drying shrinkage compared with the other samples containing 0%, 40% and 60% HMNS contents. This study shows the potential of incorporating HMNS as value source material for geopolymer production.

SIMULTANEOUS OPTIMISATION OF DRYING PARAMETERS OF CERAMIC BODIES

This study deals with the mineralogical, physico-chemical and geotechnical analyses of representative Aptian clays in the north-east of Tunisia. X-ray diffraction reveals a predominance of illite (50-60 wt.%) associated to kaolinite and interstratified illite/smectite. The accessory minerals detected in raw materials are quartz, calcite and Na-feldspar. The average amounts of silica, alumina and alkalis are 52, 20 and 3.5 wt.%, respectively. The contents of lime and iron vary between 4 and 8 wt.%. Physical analyses show that the cation exchange capacity is 34.1-45.7meq/100g of air-dried clay. The plasticity test shows medium values of plasticity index (16-a28 wt.%). The linear drying shrinkage is weak (less than 0.99 wt.%) which makes these clays adapt to fast drying. The firing shrinkage and the expansion are limited. A lower firing and drying temperature can be translated into significant energy savings. Currently, these clays are used in the industrial process for the manufacturing of the earthenware tiles. For the better exploitation of the materials and improvement of production conditions, a mathematical formalism is established for the drying parameters. The regression models relate drying shrinkage (d), bending strength after drying (b) and residual moisture (r) with the moisture (m) and the pressing pressure (p).

Effect of aging temperature on the porosity characteristics of subcritically dried silica aerogels

Silica aerogels were synthesised by subcritical drying technique which involves controlled solvent exchange and aging of the wet gel in silane solution followed by drying under controlled conditions. Effect of temperature of aging in silane solution on the porosity characteristics of silica aerogels and the thermal pore stability of the resultant gels were investigated. Aging in silane solution leads to an increased degree of condensation reactions, siloxane crosslinking and the dissolution and reprecipitation of silica monomers to the gel structure and enhances the total strength of the gel. Thermal aging of the wet gel have a pronounced effect on bulk density, linear drying shrinkage, surface area and pore volume. As the temperature of aging increases the bulk density decreases whereas the surface area and pore volume were found to increase. We could achieve a surface area of 1040 m2/g, pore volume 1.2 cc/g and an average pore size of 49 A corresponding to an aging temperature of 70 °C. Thermal pore stability of the gel was found to be up to 700 °C above which densification of SiO2 gel starts. The novel findings will help in tailoring the process parameters to prepare mesoporous oxides from sol–gel precursors with specific pore features.

Effect of nanoparticulate boehmite sol as a dispersant for slurry compaction of alumina ceramics

This work reports the use of monohydroxy aluminium oxide particulate sol [boehmite, AlOOH], as a dispersing medium for slurry compaction of submicron-sized alumina powders. Nanoparticulate boehmite sol, at controlled pH conditions, resulted in homogeneously dispersed alumina suspension which could be compressed into a definite shape by applying simple pressure. The partially flocculated boehmite sol at pH 6.2 acts as good dispersant and resulted in alumina–boehmite solids loading >80 wt.%. The alumina dispersed in boehmite sol containing 17.24 vol.% boehmite concentration showed maximum green and sintered density. The maximum theoretical green density was 63% and the maximum linear drying shrinkage was <3%. The maximum theoretical sintered density was about 97% at 1450°C. The slurry compaction resulted in high-density, fine-grained, sintered alumina having average grain size at about 2 μm. The nanoparticulate boehmite sol was found to be a matrix compatible dispersant for alumina ceramics and yields higher solid loading and particle packing under slurry pressing.

Gel Casting of Alumina using Boehmite as a Binder

The process for alumina gel casting was developed using an inorganic binder The monohydroxy aluminium oxide (boehmite, AlOOH) was incorporated with ultrafine alumina of particles (0·5 μm) and the slurry rheology was studied and presented. The effect of boehmite in slurry viscosity was observed with respect to different amounts of boehmite and time. The alumina 54 vol% slurry with 10 wt% boehmite showed the viscosity of 880 mPa s at 93 s −1. An external coagulating agent, HMTA, was incorporated with alumina–boehmite slurry and the effective change in slurry viscosity with respect to concentration and time was studied. The addition of HMTA results in faster gelation and the optimum concentration was determined as 0·21 mol L −1. The alumina gelcast body was dried under humidity conditions at 40°C, RH 70%. The defect free dried green body was obtained and the total linear drying shrinkage was calculated as 3·2% and the green density observed was 59·3% of theoretical value. The sintered density of 98% (TD) was achieved at 1450°C in 2 h. The mechanical hardness of sintered alumina measured as 2286 kg mm −2. The sintered ceramic showed an extremely fine grained microstructure with an average grain size <2 μm. The boehmite acts as an excellent binder and sintering aid for alumina ceramics.