Inorganic Polymer Cement Research Articles

: Expansivity mitigation of black clay soil using agro-waste based inorganic polymer cement for flexible pavement subgrade

: Expansivity mitigation of black clay soil using agro-waste based inorganic polymer cement for flexible pavement subgrade

POTENTIAL OF GEOPOLYMER COATING FOR LIGHTWEIGHT AGGREGATE VIA MILLING AND DIPPING METHOD: A REVIEW

The high demand for construction materials and building products, particularly aggregates, necessitates the development of innovative as the natural aggregate resource depletes. Lightweight aggregates are one of the alternatives has meet industry demand with low apparent density, excellent thermal insulation property and fire protection. Unfortunately, lightweight aggregate has a high-water absorption rate, which results in low strength and high porosity. These conditions had a negative impact on the qualities of fresh concrete, such as strength, slump, and cracking. Surface coating is thought to be a good way to prevent water absorption by lightweight particles, which lowers the concrete's performance. To reinforce the concrete, inorganic polymer composite material and cement were commonly employed to coat lightweight particles. The article presents a review on current issues facing by lightweight aggregate, mix proportion of geopolymer coating (aluminosilicate raw materials, alkaline activator ratio) and coating method (milling and dipping). This review has highlighted performance of lightweight aggregate for concrete application can be enhanced by approaching geopolymer coating as surface coating.

Valorization of marble powder wastes using rice husk ash to yield enhanced-performance inorganic polymer cements: Phase evolution, microstructure, and micromechanics analyses

The challenge for sustainable development is now constraining scientists, and policymakers to consider alternative materials and processes requiring low energy consumption and low emissions while prioritizing local materials and industrial waste recycling. This study investigates ways to valorize marble waste powders to design a new class of inorganic polymer cement. These powders are among the most important solid wastes globally, and in the Italian island of Sardinia they create a disposal problem. When these powders, which are rich in calcium silicate hydrate (C–S–H) phases, are incorporated into the geopolymer synthesis, this gives rise to a mix between C–S–H and alkali metal aluminosilicate hydrate (M-A-S-H) systems that are the focus of this study. In detail, C–S–H systems are prepared with various Ca/Si ratios, including CS, C 2 S, and C 3 S. The microstructure and mechanical properties are investigated using X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy, along with density methods (mercury intrusion porosimetry), macroscopy mechanical testing methods (flexural strength tests) and nanoscale mechanical testing methods (indentation testing and scratch testing). The resulting inorganic polymer cements exhibit both an amorphous and a crystalline phase containing sodium-calcium-aluminum-silicate hydrate N–C-A-S-H. The fraction of the crystalline phase increases when the silica content decreases, from CS to C 3 S, and when the C–S–H fraction increases. In turn, the crystalline phase dictates the pore structure and mechanical properties. Specifically, a homogeneous and compact microstructure with low porosity is observed. The flexural strength ranges from 5.8 to 8.7 MPa, the elastic modulus ranges from 10 to 17 GPa, and the fracture toughness ranges from 0.23 to 0.48 MPa m 1/2 . In general, the lower the silica percentage of the calcium-silicate hydrates and the higher the fraction of calcium silicate hydrate are, the higher the flexural strength, elastic modulus, and fracture toughness. The underlying mechanism for the observed stiffening, strengthening, and toughening is the insertion of aluminum in the C–S–H defect sites to yield C-A-S-H, along with the formation of sodium silicate gel from excess colloidal silica, which contributes to the reduction in gel pores and matrix densification. The values of porosity, density, and mechanical properties suggest that inorganic polymer cements derived from marble wastes are promising candidates for innovative low-temperature and low-density binders with low carbon footprint satisfying both the requirements of sustainability and the local material concept. • Rice husk ash is suitable to increase the reactivity of marble powder wastes. • The marble-derived inorganic polymer cements show an enhancement in strength. • Two phases co-exist: amorphous metakaolin geopolymer and crystalline N–C-A-S-H. • The N–C-A-S-H crystalline phase content increases with the C–S–H and Ca content. • Marble derived inorganic polymer cements are promising Portland cement alternatives.

Mechanical and physical properties of inorganic polymer cement made of iron-rich laterite and lateritic clay: A comparative study

In this work, two different laterites (iron contents of 13.07 and 49.34 wt%, respectively, for lateritic clay, LAC, and iron-rich laterite, LAI) were selected and calcined at 600 °C. The obtained calcined laterites, namely LAI600 and LAC600, were separately mixed with an alkaline solution (silicate modulus of 1.35) or an acidic solution (phosphoric acid solution at pH ≤ 2) for the synthesis of inorganic polymer products. The fabricated products were cured at 20 °C (ambient) and 40 °C (oven). The obtained results showed that the compressive strength of each series of alkaline-based inorganic polymer binder increased with ageing time (7 and 28 days) for room temperature curing, while the reverse trend was noted for oven-cured specimens. The best mechanical performance was obtained when using a phosphoric acid solution, 38 and 52 ± 1 MPa; 62 and 65 ± 1 MPa at 28 days for LAC and LAI respectively. It appeared that a higher iron content within the laterite contributed to an increase in the compressive strength under acidic conditions (LAI (59 MPa) > LAC (48 MPa)) compared to the behavior obtained under alkaline conditions (LAI (6 MPa) < LAC (29 MPa)). Accordingly, the acidic products exhibited a dense structure (with lower porosity) and contained amorphous iron/aluminium phosphate phases such as berlinite (FePO4), iron hydrogen phosphate hydrate (Fe3H15(PO4)8·4H2O), ferrowyllieite (AlFe2Na2(PO4)3) and sodium iron phosphate (Na3Fe2(PO4)3) arising from the alteration of iron minerals in an acidic medium, confirmed by Mössbauer spectroscopy and electron paramagnetic resonance spectroscopy.

Preparation of drying powder inorganic polymer cement based on alkali-activated slag technology

In the alkali activated inorganic polymer preparation process, liquid water glass is used as an alkali-activator to dissolve the solid aluminosilicate precursor and form the cement material. However, liquid water glass is not convenient for storage or transportation. Developing an inorganic polymer-based powder cement (IPBPC) as a one-part mixture (“just add water”), similar to Portland cement, increases its commercial viability. Through compressive strength and heat flow analysis, this paper presents research on the mechanical properties and reaction process of slag with solid or liquid water glass; in contrast, solid water glass has better mechanical performance. The L9(34) orthogonal experiment method is used to optimize the experimental formula. According to the range analysis and SEM, this result indicates that the level of significance of factors are as follows: m(SL)/m(WG)>fly ash>water>retarder; m(SL)/m(WG) has the most significant impact on the 7-day compressive strength of the IPBPC sample. The 29Si solid-state NMR patterns demonstrate that in the IPBPC sample with m(SL)/m(WG)=5:1, primarily Q2 and Q2(1Al), the Al can incorporate into the gel. The optimum formula is as follows: m(SL)/m(WG)=5:1, retarder 7%, fly ash 10%, and water 28%. The 7-day compressive strength of the optimum composition is 67.38MPa, the initial setting time is 150min, and the final setting time is 230min and meets the construction conditions.

Cleaner production of the lightweight insulating composites: Microstructure, pore network and thermal conductivity

Inorganic polymer cement paste was used as cleaner binder for the design of lightweight matrices as insulating envelopes and panels in building and construction industries. Sponge-like structure with a homogeneously distributed pore network, low density and low thermal conductivity permitted to classify the geopolymer–wood fiber composites promising clean insulating materials. Matrices with the density ∼0.79g/cm3, bi-axial four-point flexural strength of ∼4MPa presented thermal conductivity between 0.2 and 0.3W/(mK). The possibility of substituting the sodium silicate with rice ash-NaOH system and the efficiency of the matrices to constitute an effective tortuous road for the thermal gradient improved the sustainability and quality of this new class of products. The pores network and the microstructure approximated by a spatial periodic geometry suggested a “macro transport” mechanism to explain the movement of heat across the matrix of light geopolymer composite.

Metakaolin-based inorganic polymer composite: Effects of fine aggregate composition and structure on porosity evolution, microstructure and mechanical properties

This paper examines the phase transformation, pore evolution, microstructural and mechanical changes that occur in inorganic polymer cement (IPC) in the presence of three different grade of fine aggregates (ф<100μm) of ladle slag, nepheline syenite and quartz sand. Experimental results indicate that polycondensation was enhanced in nepheline syenite based specimens, compared to quartz sand, due to the increase in HMAS phases in relation to the dissolution and interaction of amorphous/disordered fraction of aggregates. HCS and HCAS with HMAS phases were identified in the ladle slag based specimens. The formation of these new phases reduced both the cumulative pore volume and pores size. The apparent increase in volume of capillary pores in ladle slag based specimens was explained by the residual bubbles from the carbonates included in raw slag. The flexural strength of the inorganic polymer cement increases from 4MPa to 4.2, 4.8 and 6.8MPa with the addition of 20wt% of quartz sand, nepheline syenite and ladle slag respectively. These values increase significantly between 28 and 180days of curing (9.1MPa for ladle slag and 10.0MPa for nepheline syenite). It was concluded that fines can be used to remove the HM and poorly bounded alumina oligomers in metakaolin based inorganic polymer matrices and improve the interfacial zone for the design of an optimum grade and high-performance composites.

Inorganic Polymer Cement from Fe-Silicate Glasses: Varying the Activating Solution to Glass Ratio

Large volumes of Fe-silicate glasses—slags—are produced as residues of metal production and waste treatment processes. It would be interesting if these materials could become an alternative group of precursors for the synthesis of inorganic polymer (IP) cements. This paper investigates the polymerisation of Fe-silicate glasses of composition (in wt%) SiO2: 40; FeO: 30; CaO: 15; Al2O3: 8 and an activating solution of composition (in wt%) Na2O: 15; SiO2: 13; H2O: 72. The mass ratio of the activating solution to the glass (L/S) was varied from 0.3 to 1.0 and the effect on the IP chemistry, microstructure and properties was investigated. Despite the high Fe and low Al contents of the glass, an IP cement could be synthesised, resistant to water dissolution and delivering mortars of compressive strength >52 MPa after 28 days curing at room temperature when using a L/S ratio of 0.45. Lowering the ratio from 1.00 to 0.45 results in a significant improvement in compressive strength, a lower porosity and when immersed in water, Na dissolution is decreased and water pH is lower. Microstructural investigation indicates that when the amount of activating solution is decreased, the degree of glass dissolution is lower resulting in less IP formation and a more homogeneous IP chemistry. Compared to higher L/S ratios, the IP mortar has a more densely packed microstructure of partially dissolved glass and sand aggregates bound by the IP matrix. At lower L/S ratios, the formation of micro scale shrinkage cracks in the IP matrix is strongly reduced, while at higher L/S ratios, shrinkage cracking is more pronounced and individual micro-cracks connect to form more pronounced large scale cracks. At a L/S ratio of 0.45, the IP cement is composed of 90 wt% Fe-silicate glass and only 10 wt% Na-silicate (% of powder mix) and it is indicated that this percentage can still be reduced. As 90 wt% of this IP cement is composed of an industrial residue and as curing is performed at ambient temperatures, its production is expected to have important ecological and economic benefits.

Design of inorganic polymer cements: Effects of matrix strengthening on microstructure

The effects of bulk composition and microstructure on strengthening mechanisms and fracture resistance were investigated for metakaolin based geopolymers. Crack initiation and propagation under mechanical and environmental stresses were correlated to pore size distribution and bulk composition. Based on IR spectra and porosity analysis, it was observed that capillary pores and the nature of alkali-aluminosilicate hydrated named polysialates (H–M–A–S) determine cracks initiation site in the Al-rich geopolymer samples with low Si/Al molar ratio (range 1.23–1.5). These samples exhibited low flexural strength, Young modulus and Impact toughness as well as delayed failure under environmental stresses. Increasing the Si/Al molar ratio (range 1.79–2.42) improved the flexural strength and Impact toughness. Formation of more polymerized H–M–A–S phases contributed to strengthening the matrices and hinder axial cracks; consequence of toughening mechanisms developed by the coarsening on molecular scale of H–M–A–S.

Bulk composition and microstructure dependence of effective thermal conductivity of porous inorganic polymer cements

Experimental results and theoretical models are used to assess the effective thermal conductivity of porous inorganic polymer cements, often indicated as geopolymers, with porosity between 30 and 70. vol.%. It is shown that the bulk chemical composition affects the microstructure (grains size, pores size, spatial arrangement of pores, homogeneity, micro cracks, bleeding channels) with consequently the heat flow behaviour through the porous matrix. In particular, introduction of controlled fine pores in a homogeneous matrix of inorganic polymer cements results in an increase of pore volume and improvement of the thermal insulation. The variation of the effective thermal conductivity with the total porosity was found to be consistent with analytical models described by Maxwell-Eucken and Landauer.

Pore solution composition and alkali diffusion in inorganic polymer cement

Extraction of pore solutions from hardened inorganic polymer cement (“geopolymer”) paste samples shows that the pore network of these materials is rich in alkali cations and has pH > 13, with a relatively low dissolved Si concentration. However, there is little soluble Ca available in these materials to play a buffering role similar to Ca(OH) 2 or high-Ca C–S–H in hydrated Portland cements, meaning that preventing alkali loss is essential in ensuring the protection of reinforcing steel. It has been seen previously that calcium in an inorganic polymer cement binder is important in the formation of a low-permeability pore system; alkali diffusion measurements confirm these observations and highlight the role of Ca in reducing effective alkali diffusion coefficients by up to an order of magnitude. This is crucial for the durability of inorganic polymer concretes containing steel reinforcement, as it appears that the use of calcium-containing raw materials will be highly preferable.

The evolution of strength and crystalline phases for alkali-activated ground blast furnace slag and fly ash-based geopolymers

The increase in strength and evolution of crystalline phases in inorganic polymer cement, made by the alkali activation of slag, Class C and Class F fly ashes, was followed using compressive strength test and synchrotron X-ray diffraction. In order to increase the crystallinity of the product the reactions were carried out at 80 °C. We found that hydrotalcite formed in both the alkali-activated slag cements and the fly ash-based geopolymers. Hydroxycancrinite, one member of the ABC-6 family of zeolites, was found only in the fly ash geopolymers. Assuming that the predominantly amorphous geopolymer formed under ambient conditions relates to the crystalline phases found when the mixture is cured at high temperature, we propose that the structure of this zeolitic precursor formed in Na-based high alkaline environment can be regarded as a disordered form of the basic building unit of the ABC-6 group of zeolites which includes poly-types such as hydroxycancrinite, hydroxysodalite and chabazite-Na.

Spatial distribution of pores in fly ash-based inorganic polymer gels visualised by Wood’s metal intrusion

Inorganic polymer cements, or ‘geopolymers’, are now finding use as a replacement for Portland cement in concrete production, and have a complex pore structure which has proven difficult to measure accurately by gas or mercury porosimetry. These materials consist of an alkali aluminosilicate-based gel binder phase, within which are embedded unreacted precursor (usually coal fly ash and/or blast furnace slag) particles. Impregnation of the inorganic polymer samples with Wood’s metal, a low-melting-point alloy which solidifies at room temperature, and examination by scanning electron microscopy, allows both the size of pores and their physical distribution within the gel to be determined. Pore sizes as small as 10 nm are directly observable in high-resolution imaging. Much of the difficulty in applying standard porosimetry techniques to inorganic polymers may be identified as being related to the presence of numerous ‘ink-bottle’ pores, as well as the very wide distribution of pore diameters (spanning several orders of magnitude). The effect of gel chemistry on pore structure, and in particular the presence of calcium in the inorganic polymer formulation, is also considered.

Microscopy and microanalysis of inorganic polymer cements. 1: remnant fly ash particles

Accurate and precise electron microscopic analysis of the remnant solid precursor (fly ash and blast furnace slag) particles embedded in an inorganic polymer cement (or “fly ash geopolymer”) provides critical information regarding the process of gel binder formation. Differential solubility of phases in the fly ash is seen to be important, with insoluble mullite crystals becoming exposed by the retreat of the surrounding glassy phases. High-iron particles appear to remain largely unreacted, and the use of sectioned and polished specimens provides a view of the inside of these particles, which can show a wide variety of phase separation morphologies and degrees of intermixing of high iron and other phases. Calcium appears to be active in the process of alkali activation of ash/slag blends, although the competitive and/or synergistic effects of ash and slag particles during the reaction process remain to be understood in detail.

Microscopy and microanalysis of inorganic polymer cements. 2: the gel binder

By scanning electron microscopy and microanalysis of fly ash-based and mixed fly ash-slag inorganic polymer cement (i.e., “fly ash geopolymer”) binders, a more detailed understanding of the gel structure and its formation mechanism have been developed. The binder is predominantly an aluminosilicate gel charge balanced by alkali metal cations, although it appears that calcium supplied by slag particles becomes relatively well dispersed throughout the gel. The gel itself is comprised of colloidal-sized, globular units closely bonded together at their surfaces. The microstructure of the binder resulting from hydroxide activation of fly ash is much less uniform than that which forms in a corresponding silicate-activated system; this can be rationalized in terms of a newly developed explanation for the differences in reaction mechanisms between these two systems. In hydroxide activation, the newly formed gel phase nucleates and grows outwards from the ash particle surfaces, whereas the high silica concentration in a silicate-activated system enables a more homogeneous gelation process to take place throughout the inter-particle volume.

Seismic performance of inorganic polymer concrete joints

Because of the large quantities of carbon dioxide released during cement production, the concrete industry is a major emitter of greenhouse gases worldwide. Inorganic polymer cement has the potential to replace Portland cement as a binder in concrete, which could reduce greenhouse gas emissions due to cement production by approximately 85%. This paper assesses the performance of three interior beam–column joints constructed using inorganic polymer concrete. The joints tested were designed using existing standards, and their performance was compared with the performance of a companion joint constructed from Portland cement concrete. Inorganic polymer concrete mixed at a precast concrete factory using conventional equipment was found to have predictable properties and to behave similarly to Portland cement concrete. Cyclic testing of beam–column joint subassemblies showed that the hysteretic, bond and energy dissipation characteristics of inorganic polymer concrete joints were identical to respective characteristics of Portland cement concrete joints. It was concluded from these results that inorganic polymer beam–column joints can be safely designed to resist earthquake-induced forces using existing New Zealand design standards.