Behzad Nematollahi

Tensile Strain Hardening Behavior of PVA Fiber-Reinforced Engineered Geopolymer Composite

AbstractThis paper is aimed to improve the mechanical properties (namely compressive and tensile strengths) of a recently developed fly ash-based engineered geopolymer composite (EGC) with relatively low-concentration activator combinations. In this regard, four different activator combinations (including two Na-based solutions and one K-based activator solution, and one lime-based activator combination in the form of powder) were used to develop the fly ash-based EGCs exhibiting strain hardening behavior under uniaxial tension. Randomly oriented short polyvinyl alcohol (PVA) fibers (2% v/v) were used to reinforce the relatively brittle low-calcium (Class F) fly ash-based geopolymer matrix. The matrix and composite properties of the developed fly ash-based EGCs [including workability of the fresh matrix, density, compressive strength, matrix fracture properties (comprising elastic modulus, fracture toughness, and composite crack tip toughness), and uniaxial tensile behavior] were evaluated. A counterpart ...

Properties of Fresh and Hardened Glass Fiber Reinforced Fly Ash Based Geopolymer Concrete

This paper evaluates the effects of glass fiber addition on the properties of fresh and hardened fly ash based geopolymer concrete (GPC) activated by 8 M NaOH solution (28.6%) + Na2SiO3 (71.4%) with a SiO2/Na2O ratio of 2.0. Glass fibers at the dosages of 0.50%, 0.75%, 1.00% and 1.25% by volume of concrete were added to the GPC mix. The properties of fresh and hardened glass fiber reinforced fly ash based GPC in terms of workability, density, compressive and flexural strengths were compared with those of the fly ash based GPC without using glass fiber. The experimental results indicated that inclusion of the glass fibers resulted in decrease of the workability but increase of the density, compressive and flexural strengths of the fly ash based GPC with increased fiber content.

Current progress of 3D concrete printing technologies

The construction industry is expected to go through large transformations since construction automation is anticipated to drastically alter standard processing technologies and could lead to possible disrupting technologies such as 3D concrete printing (3DCP). While 3D printing techniques have been successfully applied in a wide range of industries such as aerospace and automotive, its application in concrete construction industry is still in its infancy. 3DCP can allow freeform construction without the use of expensive formwork, which in return offers excellent advantages compared to conventional approach of casting concrete into a formwork. In the last few years, different 3DCP technologies have been developed. This paper presents the current progress of 3DCP technologies. An innovative methodology recently developed by the authors of this study for formulating geopolymer-based material for the requirements and demands of commercially available powder-based 3D printers is also briefly presented.

Effect of superplasticizers on workability of fly ash based geopolymer

This paper evaluates the effect of different commercial superplasticizers (SPs) usually used for ordinary Portland cement concrete production such as naphthalene, melamine (second generation of products) and modified Polycarboxylate based (latest generation) on the workability of a class F fly ash paste activated by 8 M NaOH solution (28.6 %) + Na2SiO3 (71.4 %) with a SiO2/Na2O ratio of 2.0. These SPs at a dosage of 1 % by mass of fly ash were added to the fresh paste and flowability of the activated fly ash paste was measured by mini slump test and compared with that of the paste without using any SP. The experimental results indicated that each SP affected the workability of the fly ash geopolymer differently. When the NaOH + Na2SiO3 used as the activator the modified Polycarboxylate based SPs (latest generation) was the most efficient type which increased the relative slump of the paste up to 45 % with reference to the paste without using any SP.

Effect of Delay Time on the Mechanical Properties of Extrusion-Based 3D Printed Concrete

The extrusion-based 3D printing method is one of the main additive manufacturing techniques used in the construction industry which is capable of producing large-scale building components with complex geometries without the use of the expensive formwork. The mechanical properties of the printed concrete component are very much unlike the conventionally cast concrete. Therefore, the properties of these are important for the design of structures built with 3D printing process. In this study, a custom-made apparatus was used to simulate extrusion-based 3D printing process. Layered specimens with 10, 20 and 30 minutes delay time (i.e. the printing time interval between layers) have been printed using tailored conventional concrete mixture. Mechanical properties including compressive, flexural and inter-layer bonding strengths have been measured and the effect of delay time on the mechanical properties has been

Hardened Properties of 3D Printable ‘One-Part’ Geopolymer for Construction Applications

This paper reports the hardened properties of an extrusion-based 3D printable ‘one-part’ geopolymer for construction applications. To date, all of the 3D printable geopolymers reported in the literature had ‘two-part’ mix formulations, made by using liquid activators. In contrast, the 3D printable geopolymer developed in this study has a ‘one-part’ (just-add-water) mix formulation, made by using a small amount of solid activator instead of the commonly used liquid activators. Handling a small amount of solid activators instead of large quantities of user-hostile liquid activators significantly enhances commercial viability and large-scale application of the 3D printable geopolymers in construction industry. Effects of print-time interval on the inter-layer strength, along with compressive and flexural strengths of the developed 3D printed ‘one-part’ geopolymer in different directions were investigated. Specimens were printed with 2 and 15 min delay times (print-time intervals). Compressive, flexural and inter-layer strengths of the 3D printed ‘one-part’ geopolymer were measured. The results showed that the print-time interval had a significant effect on the inter-layer strength of the 3D printed ‘one-part’ geopolymer. However, the effect of the print-time interval on the compressive and flexural strengths of the 3D printed ‘one-part’ geopolymer was negligible. The results also showed that the compressive and flexural strengths of the 3D printed ‘one-part’ geopolymer depended on the loading direction.

Fresh and Hardened Properties of 3D Printable Geopolymer Cured in Ambient Temperature

This paper reports the fresh and hardened properties of an ambient temperature cured 3D printable geopolymer suitable for extrusion-based 3D concrete printing process. Effects of several key geopolymer synthesis parameters including type of alkaline activator (sodium (Na)-based versus potassium (K)-based), mass ratio of silicate to hydroxide solutions, viscosity and SiO2/M2O ratio (where M = Na or K) of silicate solution on extrudability, open time, shape retention ability and compressive strength of the 3D printable geopolymers were investigated. The results revealed that the type of alkaline activator solution and SiO2/Na2O ratio of the silicate solution had a significant influence on the open time and shape retention ability of the mixtures. The parameters investigated in this study did not have significant effect on the extrudability of the mixtures. The Na-based activators resulted in higher compressive strength of 3D printed geopolymer than the K-based activators. The 3D printable geopolymer mixture made by 8.0 M NaOH solution (25% w/w) and Na2SiO3 solution (75% w/w) with a SiO2/Na2O ratio = 2.0 exhibited the highest compressive strength of 16.6 MPa when cured for only 3 days in the ambient temperature.

Compressive Strength and Dimensional Accuracy of Portland Cement Mortar Made Using Powder-Based 3D Printing for Construction Applications

An innovative methodology has recently been developed by the authors of this study for geopolymer formulations for the requirements and demands of commercially available powder-based 3D printers. In this study, the formulation is extended to conventional Portland cement to expand the scope of printable materials that can be used in the commercially available powder-based 3D printers for construction applications. A Portland cement-based powder composed of Portland cement, amorphous calcium aluminate and fine silica sand was developed for powder-based 3D printing process. Effects of different printing parameters including binder saturation level (100%, 135% and 170%) and shell to core ratio (1:1 and 1:2) on dimensional accuracy and compressive strength of the green specimens have been investigated. A compressive strength of up to 8.4 MPa was achieved for the ‘green’ 3D printed samples before any post-processing process. The results indicated that the increase in the binder saturation level and the change in the Shell/Core ratio from 1:1 to 1:2 significantly increased the compressive strength, but considerably reduced the linear dimensional accuracy of the green samples. The compressive strength and linear dimensional accuracy of the green samples exhibited an anisotropic behavior, depending on the testing direction.

Sustainable Fiber-Reinforced Strain-Hardening Composites Using Geopolymer as ‘Complete’ Replacement of Portland Cement

Strain-hardening cementitious composite (SHCC) is a special class of high-performance fiber-reinforced cementitious composites which exhibits strain-hardening behavior with very high tensile ductility of up to 5% at a moderate fiber content (2% or less by volume). Typically high cement content is used in this composite resulting in high autogenous shrinkage, heat of hydration, and cost. In addition, the associated increase in the CO2 emissions and embodied energy arising from the production of ordinary Portland cement (OPC) can compromise sustainability credentials of SHCCs. In the recent years the authors of this study developed an OPC-less strain-hardening geopolymer composite (SHGC). Geopolymer is used as ‘complete’ replacement of OPC in SHGC composition. Geopolymer is a sustainable alternative to OPC which emits at least 80% less CO2 and requires about 60% less energy as compared to production of OPC. The developed SHGCs are promising sustainable alternatives to typical SHCC, expecting to promote sustainability of the infrastructures via concurrent improvements of material greenness and infrastructure durability through very high tensile ductility and tight crack width control. This paper presents an overview of the authors’ research work on development and investigation of properties of SHGCs. The paper also presents a quantitative comparison of material sustainability performance of the developed SHGCs with typical SHCC.