Effects of Reactive MgO on the Reaction Process of Geopolymer

In order to compensate for the shrinkage of geopolymer pastes uniformly, reactive MgO powders are evenly dispersed in the geopolymer. The deformation performance, mechanical properties, microstructure and components of geopolymer pastes with reactive MgO are characterized. The effects of the content and the activity of MgO are discussed. The results indicate that the chemical shrinkage, autogenous shrinkage and drying shrinkage decrease with the addition of reactive MgO. MgO reacted with water, and fine Mg(OH)2 crystals forms as a geopolymer paste. Mg(OH)2 produces uniform expansion, which refines the pore size of pastes and the compressive strength increases. The shrinkage of the geopolymer pastes is thus effectively compensated.

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Effect of Steel Slag on Shrinkage Characteristics of Calcium Sulfoaluminate Cement

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1036.263 ◽

2021 ◽

Vol 1036 ◽

pp. 263-276

Author(s):

Hao Ran Huang ◽

Yi Shun Liao ◽

Siraj Ai Qunaynah ◽

Guo Xi Jiang ◽

Da Wei Guo ◽

...

Keyword(s):

Compressive Strength ◽

Relative Humidity ◽

Cement Paste ◽

Steel Slag ◽

Autogenous Shrinkage ◽

Drying Shrinkage ◽

Chemical Shrinkage ◽

Calcium Sulfoaluminate Cement ◽

Calcium Sulfoaluminate ◽

Slag Content

The effects of steel slag with 0, 10%, 20 % and 40% content on the chemical shrinkage, autogenous shrinkage, internal relative humidity, and drying shrinkage of calcium sulfoaluminate cement paste were studied. The results show that the compressive strength of calcium sulfoaluminate cement paste at an early stage decreases gradually when the content of steel slag increases. When the steel slag content is 0 and 10%, the compressive strength of hardened cement pastes gradually decreases at 90 and 180 days, but the samples with steel slag content of 20% and 40% maintain the compressive strength growth within 180 d. With the extension of curing period, the gap of compressive strength is gradually narrowed. The autogenous shrinkage decreases with the increase of steel slag content and has a good linear relationship with the relative humidity inside the paste. The proportion of autogenous shrinkage to chemical shrinkage is deficient, and most chemical shrinkage occurs in the form of the pore volume. Although the trends of drying shrinkage and autogenous are consistent, the former is more severe than the latter.

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Enhancing Density-Based Mining Waste Alkali-Activated Foamed Materials Incorporating Expanded Cork

CivilEng ◽

10.3390/civileng2020029 ◽

2021 ◽

Vol 2 (2) ◽

pp. 523-540

Author(s):

Imed Beghoura ◽

Joao Castro-Gomes

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

Pore Size ◽

Physical And Mechanical Properties ◽

Critical Parameters ◽

Porous Structures ◽

Foaming Agent ◽

Al Powder ◽

Highly Porous ◽

Alkali Activated

This study focuses on the development of an alkali-activated lightweight foamed material (AA-LFM) with enhanced density. Several mixes of tungsten waste mud (TWM), grounded waste glass (WG), and metakaolin (MK) were produced. Al powder as a foaming agent was added, varying from 0.009 w.% to 0.05 w.% of precursor weight. Expanded granulated cork (EGC) particles were incorporated (10% to 40% of the total volume of precursors). The physical and mechanical properties of the foamed materials obtained, the effects of the amount of the foaming agent and the percentage of cork particles added varying from 10 vol.% to 40% are presented and discussed. Highly porous structures were obtained, Pore size and cork particles distribution are critical parameters in determining the density and strength of the foams. The compressive strength results with different densities of AA-LFM obtained by modifying the foaming agent and cork particles are also presented and discussed. Mechanical properties of the cured structure are adequate for lightweight prefabricated building elements and components.

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Preparation of Porous HA Bioceramics by Gelcasting and Pressureless Sintering

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.335-336.1454 ◽

2011 ◽

Vol 335-336 ◽

pp. 1454-1458

Author(s):

Jing Xian Zhang ◽

Bi Qin Chen ◽

Dong Liang Jiang ◽

Qing Ling Lin ◽

Zhong Ming Chen ◽

...

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

Pore Size ◽

Pressureless Sintering ◽

High Compressive Strength ◽

Microstructure And Properties ◽

Pmma Beads ◽

Average Compressive Strength

In the present work, porous HA scaffolds with well controlled pore size, porosity and high compressive strength were prepared by aqueous gelcasting. PMMA beads with different size were used as the pore forming agent. The compositions, microstructure and properties of porous HA bioceramics were analyzed by XRD, SEM, Hg porosimetry etc. The mechanical properties were also tested. For scaffolds with the porosity as 70%, the average compressive strength was 11.9±1.7 MPa. Results showed that glecasting process can be used for the preparation of porous HA biomaterials with well controlled pore size and improved mechanical properties.

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Effect of Filler Type on the Thermo-Mechanical Properties of Metakaolinite-Based Geopolymer Composites

Materials ◽

10.3390/ma13102395 ◽

2020 ◽

Vol 13 (10) ◽

pp. 2395 ◽

Cited By ~ 2

Author(s):

Jan Kohout ◽

Petr Koutník

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

Flexural Strength ◽

Pore Size ◽

Average Pore Size ◽

Diffraction Method ◽

Thermal Exposure ◽

Total Shrinkage ◽

Pore Size Distributions ◽

Geopolymer Composites

Metakaolinite-based geopolymer binder was prepared at room temperature by mixing calcined claystone and potassium alkaline activator. Various granular inorganic fillers were added, amounting to 65 vol % to form geopolymer composites. The effect of four types of fillers (sand quartz, chamotte, cordierite, and corundum) on the thermo-mechanical properties of metakaolinite-based geopolymer composites were investigated. The samples were also examined by an X-ray diffraction method to determine their phase composition. The pore size distributions were determined by a mercury intrusion porosimeter. The XRD revealed the crystallization of new phase (leucite) after thermal exposure at 1000 °C and higher. Geopolymer binders had low mechanical properties (flexural strength 2.5 MPa and compressive strength 45 MPa) and poor thermo-mechanical properties (especially high shrinkage—total shrinkage 9%) compared to geopolymer composites (flexural strength up to 13.8 MPa, compressive strength up to 95 MPa and total shrinkage up to 1%). The addition of fillers reduced the shrinkage of geopolymers and improved their mechanical properties. The results have shown that the compressive strength tested in situ and after exposure to high temperature are in conflict. Geopolymer composites with the addition of chamotte had the best mechanical properties before and after thermal exposure (compressive strength up to 95 MPa). The average pore size diameters increased with the increasing temperature (from 10 nm to approx. 700 nm). The fillers addition decreased the pore volume (from 250 mm3/g to approx. 100 mm3/g).

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Effect of Pore Structure on Thermal Conductivity and Mechanical Properties of Autoclaved Aerated Concrete

Materials ◽

10.3390/ma14020339 ◽

2021 ◽

Vol 14 (2) ◽

pp. 339

Author(s):

Gonglian Chen ◽

Fenglan Li ◽

Pengfei Jing ◽

Jingya Geng ◽

Zhengkai Si

Keyword(s):

Mechanical Properties ◽

Thermal Conductivity ◽

Compressive Strength ◽

Pore Structure ◽

Pore Size ◽

Base Material ◽

Test Results ◽

Foam Stabilizer ◽

Base Materials ◽

Aerated Concrete

With the premise of investigating mechanical properties, the thermal conductivity of autoclaved aerated concrete (AAC) is a key index of self-insulation block walls for building energy conservation. This study focused on the effect of pore structures on the mechanical performance and thermal conductivity of AAC with the comparison of AAC base materials. Different kinds of AAC and their base materials were prepared and experimentally investigated. While maintaining a consistent mix proportion of the AAC base material, the pore structure of AAC was changed by the dosage of aluminum power/paste, foam stabilizer, and varying the stirring time of aluminum paste. The steam curing systems of AAC and the base material were determined based on SEM (Scanning Electronic Microscopy) and XRD (X-Ray Diffraction) tests. With almost the same apparent density, the pore size decreased with the increasing content of foam stabilizer, and the mixing time of aluminum paste and foam stabilizer has a great influence on pore size. The thermal conductivity test and compressive test results indicated that that pore size had an effect on the thermal conductivity, but it had little effect on the compressive strength, and the thermal conductivity of sand aeration AAC was 8.3% higher than that of fly ash aeration AAC; the compressive strength was 10.4% higher, too. With almost the same apparent density, the regression mathematical model indicates that the thermal conductivity of AAC increased gradually with the increase of pore size, but it had little effect on the compressive strength. From the test results of basic mechanical properties, the mechanical model of cubic compressive strength, elastic modulus, axial compressive strength, and splitting tensile strength was obtained. The proposed stress–strain relationship model could well describe the relationship of AAC and the base material at the rising section of the curve.

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Feasibility of Developing Sustainable Concrete Using Environmentally Friendly Coarse Aggregate

Applied Sciences ◽

10.3390/app10155207 ◽

2020 ◽

Vol 10 (15) ◽

pp. 5207

Author(s):

Chamila Gunasekara ◽

Charitha Seneviratne ◽

David W. Law ◽

Sujeeva Setunge

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

Coarse Aggregate ◽

Mechanical Performance ◽

Drying Shrinkage ◽

Strength Development ◽

Design Strength ◽

Coarse Aggregates ◽

Increasing Demand ◽

Quality Material

Quarry aggregate reserves are depleting rapidly within Australia and the rest of the world due to an increasing demand for aggregates driven by expansion in construction. The annual production of premix concrete in Australia is approximately 30 million cubic meters, while 3–5% of concrete delivered to site remains unused and is disposed of in landfill or crushing plants. The production of coarse aggregates using this waste concrete is potentially a sustainable approach to reduce environmental and economic impact. A testing program has been conducted to investigate mechanical performance and permeation characteristics of concrete produced using a novel manufactured coarse aggregate recycled directly from fresh premix concrete. The recycled coarse aggregate (RCA) concrete satisfied the specified 28-day design strength of 25 MPa and 40 MPa at 28 days and a mean compressive strength of 60 MPa at 90 days. Aggregate grading was observed to determine strength development, while low water absorption, low drying shrinkage, and higher packing density indicate that the RCA concrete is a high-quality material with a dense pore structure. The rough fracture surface of the aggregate increased the bond between C-S-H gel matrix and RCA at the interfacial transition zone. Furthermore, a good correlation was observed between compressive strength and all other mechanical properties displayed by the quarried aggregate concrete. The application of design equations as stated in Australian standards were observed to provide a conservative design for RCA concrete structures based on the mechanical properties.

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Internal Curing of Saturated Lightweight Aggregate in High Performance Combined Concrete

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.405-406.212 ◽

2009 ◽

Vol 405-406 ◽

pp. 212-218

Author(s):

Jin Zha ◽

Bei Xing Li ◽

Jin Hui Li ◽

He Gao ◽

Gong Cui

Keyword(s):

Tensile Strength ◽

Compressive Strength ◽

High Performance ◽

Volume Fraction ◽

Autogenous Shrinkage ◽

Drying Shrinkage ◽

Lightweight Aggregate ◽

Splitting Tensile Strength ◽

Hardened Concrete ◽

Chloride Permeability

This paper investigated the mechanical properties, workability, autogenous shrinkage, drying shrinkage and durability of the high performance combined aggregate concrete with the coarse aggregate replaced by the lightweight aggregate in the volume fraction from 0% to 50%. The results demonstrated that the fresh concrete with the lightweight aggregate volume fraction of 10% and 30% had good workability, but degrade with a high volume fraction of 50 %. The hardened concrete with 10% and 30% lightweight aggregate replacement had similar compressive strength and splitting tensile strength comparing to the reference concrete without adding lightweight aggregate. The concrete with 50% lightweight aggregate replacement showed decreased compressive strength and splitting tensile strength. The concrete adding lightweight aggregate exhibited less autogenous shrinkage and drying shrinkage than the reference concrete without adding lightweight aggregate. The autogenous shrinkage and drying shrinkage increased with the increasing lightweight aggregate volume fraction. The concrete containing lightweight aggregate showed good durability after 200 freezing and thawing cycles, but the chloride permeability efficiency of concrete decreased.

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Effects of Shrinkage Reducing Agent and Expansive Admixture on the Volume Deformation of Ultrahigh Performance Concrete

Advances in Materials Science and Engineering ◽

10.1155/2017/6384859 ◽

2017 ◽

Vol 2017 ◽

pp. 1-7 ◽

Cited By ~ 4

Author(s):

Su Anshuang ◽

Qin Ling ◽

Zhang Shoujie ◽

Zhang Jiayang ◽

Li Zhaoyu

Keyword(s):

Compressive Strength ◽

Autogenous Shrinkage ◽

Drying Shrinkage ◽

Reducing Agent ◽

Cementitious Material ◽

Volume Deformation ◽

Air Content ◽

Expansive Agent ◽

Reduction Effect ◽

Shrinkage Reducing Agent

This paper investigated the influences of shrinkage reducing agent and expansive admixture on autogenous and drying shrinkage of ultrahigh performance concrete (UHPC) containing antifoaming admixture. The shrinkage reducing agent was used at dosage of 0.5%, 1%, and 2% and the expansive admixture was used at dosage of 2% to 4% by mass of cementitious material. The results show that the air content of UHPC increases with the higher addition of shrinkage reducing agent and expansive admixtures. However, the fluidity, compressive strength, and shrinkage of UHPC exhibit a declining tendency. The usage of expansive agent at dosage of 4% significantly reduces the shrinkage of UHPC. The 7-day autogenous shrinkage was decreased by 16.0% and 28-day drying shrinkage was decreased by 29.5%, respectively. Shrinkage reducing agent at dosage of 2% reduced the 7-day autogenous shrinkage by 44.3% and 28-day drying shrinkage by 50.2%. Compared with expansive admixture, shrinkage reducing agent exhibits more efficient shrinkage reduction effect on UHPC.

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Chemical Shrinkage of Pastes Made with Shrinkage Reducing Admixtures

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.466.105 ◽

2011 ◽

Vol 466 ◽

pp. 105-113 ◽

Cited By ~ 1

Author(s):

António Bettencourt Ribeiro ◽

Vasco Medina ◽

Augusto Gomes ◽

Arlindo Gonçalves

Keyword(s):

High Performance ◽

High Performance Concrete ◽

Autogenous Shrinkage ◽

Drying Shrinkage ◽

Chemical Shrinkage ◽

Cement Pastes ◽

Degree Of Hydration ◽

Shrinkage Cracks ◽

Large Application ◽

Shrinkage Reducing Admixtures

Shrinkage Reducing Admixtures (SRA) are being used more often in concrete structures in order to better control shrinkage cracks. High-performance concrete, nowadays with large application, has more proneness to crack at very early age due to the lower W/C. In this type of concrete, autogenous shrinkage is usually more important than drying shrinkage. Autogenous shrinkage is due to the volume decrease inherent to binder hydration reactions. The rate of these reactions is influenced not only by the type of binder but also by the presence of chemical admixtures. It is recognized that SRA delay the hydration, being a secondary effect of this type of admixtures. In this work changes on the degree of hydration of cement pastes with SRA and different binders are presented, using the chemical shrinkage test.

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Shrinkage Behavior of Alkali-Activated Slag Cement Pastes

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.761.45 ◽

2018 ◽

Vol 761 ◽

pp. 45-48 ◽

Cited By ~ 10

Author(s):

Vladyslav Omelchuk ◽

Guang Ye ◽

Rayisa Runova ◽

Igor I. Rudenko

Keyword(s):

Autogenous Shrinkage ◽

Drying Shrinkage ◽

Chemical Shrinkage ◽

Slag Cement ◽

Cement Pastes ◽

Alkali Activated Slag ◽

Activated Slag ◽

Mineral Additives ◽

Alkali Activated ◽

Shrinkage Behavior

Nowadays, alkali-activated cements (AACs) are the most promising alternatives to ordinary portland cement (OPC). Such cements characterized by better strength and corrosion resistance that determine improved durability of materials based on them. However, the shrinkage of AAC systems is noticeably higher compared with OPC. The purpose of this work was to study the shrinkage behavior of alkali-activated slag cement (AASC) pastes. To improve early age performance of AASCs – OPC and Ca(OH)2, as mineral additives, were added to the designed cement mixtures. The properties, like, flexural and compressive strength of cement mortars, chemical shrinkage, autogenous shrinkage and drying shrinkage of cement pastes were studied. The results showed that the chemical shrinkage, autogenous shrinkage and drying shrinkage at 28 days were between 0.064 – 0.074 ml/g, 4.5 – 7.9 mm/m and 3.3 – 4.9 mm/m, respectively. The relationship between the nature of alkaline components, the type of mineral additives and the shrinkage behavior of cements were discussed.

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