Experimental Study and Numerical Simulation of the Development of the Microstructure and Permeability of Cementitious Materials

The aim of this thesis was to investigate and to simulate the development of the microstructure, porosity and permeability in hardening cement-based materials. Based on experimental information and the cement hydration model HYMOSTRUC, the microstructural details including porosity, connectivity of pores and pore size distribution were characterized. A network permeability model was built up based on the simulated microstructure and validated with the experiments.Applied Science

Basic properties of cement paste mixed with calcium hydroxide-ettringite composite type expansive additive

In this study, we targeted a calcium hydroxide and ettringite composite-type expansive additive (EA) and obtained the basic characteristics of the EA mixed cement paste in order to create a method for calculating volume expansion based on the hydration reaction of the PCEA system. Expansion strain, setting time, and compressive strength were measured. In addition, we observed the state of EA after hydration using a micro-CT scanner and scanning electron microscope, and elucidated the expansion mechanism. Our results show that strain rapidly increased and the compressive strength decreased when the replacement ratio of the EA (Crep) exceeds 6.4%. At the same time, radial cracks were generated from the hydrated EA particles, suggesting that the EA itself grew to expand the cement paste. Although no ettringite was confirmed inside the EA when the Crep was 5.1%, when the Crep was 10.3%, ettringite was formed vertically from the surface of C3A with a large amount of pores. These results show that simultaneous formation of ettringite and pores causes rapid expansion

Carbonation rates of alkali-activated and cement based concretes

The reduction of pH from ~12.5 to ~9 by carbonation of the pore solution of reinforced cementbased concrete structures results in the reinforcement corrosion. The rate of carbonation is an important input for design of the concrete cover depth and the service life prediction of reinforced concrete structures because the initiation of reinforcement corrosion is usually considered as the end of service life of concrete infrastructure. The information from the field carbonation of alkali activated concrete is in most cases limited and related to exposure shorter than 40 years. In this paper, a comparative study regarding accelerated and natural carbonation of alkali-activated concretes and cement-based concretes has been carried out. The pH and carbonation depths are periodically measured. The results show that, despite the low porosity of alkali-activated concrete with 50 wt. % slag, these concretes must have an appropriate curing in order to be used in exposure classes where carbonation is an issue, due to their lower carbonation resistance compared to cement-based concrete. Regardless the exposure conditions, the pH of carbonated alkali-activated concrete was maintained above 9. Finally, recommendations for alkali activated concrete applications and their improved carbonation resistance are given

Will ortho-enriched water increase the durability of concrete?

Water molecules exist as two spin isomers, differing by the relative orientation of the nuclear spins of the two hydrogen atoms: either antiparallel (para-water, S=0) or parallel (ortho-water, S=1) [1]. The transition between these nuclear spin states can be achieved through magnetic symmetry breaking via a field gradient across the spins applied by a suitably placed magnetic moment for a sufficiently long time [2]. The contradictory mechanisms of interaction between water or an aqueous solution and magnetic field were reviewed, especially the one expanded on Dynamically Ordered Liquid Like Oxyanion Polymers (DOLLOP) [3]. Then the state of art agreements that have been proved by reproductive experiments or theories were discussed. A new hypothesis for the magnetic effects on the interconversion of nuclear spin isomers of water at the interface of water-O2 was proposed, as well as its applicability in the structure modification of C-S-H

A review: The strength influence factors of slag and fly ash based alkali activated materials

Alkali-activated materials(AAM) are known to be environmentally friendly alternatives to cement-based materials because they can potentially reduce greenhouse gas emissions and reutilize industrial by-products. However, the application of AAM is still limited by the lack of mixture design regulation. Unlike cement, the very different chemical composition of the precusors and alkaline activators may result in a very fluctuating strength. In order to study the factors influencing the strength of slag and fly ash-based alkali-activated materials (BFS/FAAAM), and clarify their reaction mechanism, this paper reviews current knowledge about the mechanical properties and the reaction mechanisms of BFS/FA-AAM. The control factors of strength are BFS/binder ratio, Na2O/binder ratio, and SiO2/Na2O ratio. The ion concentrations, determined by these control factors, play a decisive role in the development of strength. Generally, the strength is proportional to the BFS/binder ratio. The best strength could be obtained at the optimum values of Na2O/binder ratio, and SiO2/Na2O ratio. The optimum values of the SiO2/binder ratio of BFS-AAM and FA-AAM are between 5.5%-8% and between 7-10%, respectively. The optimal values of the SiO2/Na2O ratio of BFS-AAM and FA-AAM are between 0.85-1.4 and between 0.6-1, respectively. For BFS/FA-AAM, the optimum ratio is still unknown. Further study is needed to investigate the effect of control factors on the mechanical properties of BFS/FA-AAM

Effect of reactive aggregate on the early age reaction of water-glass activated slag/fly ash mortars

Alkali activated materials (AAMs) have received worldwide attention due to its lower embodied energy and environmental impact than that of traditional cementitious materials. However, the activators with high alkalinity may raise the risk of alkali silica reaction (ASR) induced deterioration when reactive aggregates are used, which thereby limits the commercial use of AAMs. Not speaking the ASR induced long-term expansion, the early-age reaction of AAMs prepared with reactive aggregates is largely unknown. In this paper, isothermal calorimetry, thermogravimetry (TG) and mercury intrusion porosimetry (MIP) were adopted to study the heat evolution, mineralogical changes and pore structures of early-age ordinary Portland cement (OPC) mortar and water-glass activated slag/fly ash mortars. In each system, emphasis were made to understand the differences between mixtures prepared with standard inert quartz sands and reactive fine aggregates. The results show that the mortars prepared with reactive aggregates generated more heat in the wetting and dissolution stage. Particularly, the water-glass activated slag mortar presented the highest heat flow peak. Meanwhile, the results of TG illustrate that higher amount of reaction products were formed in water-glass activated mortars prepared with reactive aggregates than that with inert quartz sands. These findings suggest that the reactive aggregates are evidently involved in the early-age alkaline reaction of AAMs system

Modelling of microstructure of ASR influenced cement-based materials

ASR (alkali-silica reaction) is one of the toughest durability problems in engineering. However, the damage induced by ASR is still fairly unpredictable due to the lack of microstructural information of cement-based materials affected by ASR, while the microstructure determines the global performance. In order to fill this gap, a multiscale simulation model of ASR is under development. The basic theory and assumptions about this multiscale model can be found in [8]. This paper illustrates how the microstructure evolution of cement-based materials induced by ASR is achieved by this model. In the model, the entire chemical process including dissolution of reactive aggregate, nucleation and growth of ASR products (alkali silicate complex, calcium alkali silicate complex), is quantitatively simulated based on the kinetic and thermodynamic parameters. Furthermore, the 3D heterogeneous aggregate is numerically simulated using stereology based on the data from 2D thin-section. As a result, the dissolution degree of aggregate, the amount and location of ASR products and the porosity change can be traced. These micro parameters can be used for the simulation of crack formation in mesoscale. Similarly, the macroscale damage can be predicted based on the simulation results from mesoscale

Utilization of biomass fly ash in alkali-activated materials

This paper investigated the feasibility of using biomass fly ash (BFA) to prepare alkaliactivated slag and fly ash paste. The reference mixture was alkali-activated slag and coal fly ash (CFA) paste with a slag-to-coal fly ash ratio of 50/50. In other mixtures, coal fly ash was replaced at 40% and 100% with BFA, respectively. The results showed that the incorporation of BFA accelerated the setting of the paste, while its impact on the compressive strength was minor. XRD and FTIR results indicated that the BFA participated in the reaction process. BFA showed potential use as CFA replacement in synthesizing alkali-activated materials, which would pave a way for the valorisation of BFA

Mitigating the autogenous shrinkage of alkali-activated slag by internal curing

Alkali activated slag (AAS) has shown promising potential to replace ordinary Portland cement as a binder material. Synthesized from industrial by-products, AAS can show high strength, thermal resistance and good durability. However, AAS has been reported to exhibit high autogenous shrinkage. Autogenous shrinkage is a critical issue for building materials since it can induce micro- or macro-cracking when the materials are under restrained conditions. Hence, this work aims at mitigating the autogenous shrinkage of AAS by means of internal curing. The influences of internal curing on microstructure formation and autogenous shrinkage are investigated. The results show that internal curing provided by superabsorbent polymers is a promising way to reduce the autogenous shrinkage of AAS

Phosphomonoesterase Activities, Kinetics and Thermodynamics in a Paddy Soil After Receiving Swine Manure for Six Years

Soil phosphomonoesterase plays a critical role in controlling phosphorus (P) cycling for crop nutrition, especially in P-deficient soils. A 6-year field experiment was conducted to evaluate soil phosphomonoesterase activities, kinetics and thermodynamics during rice growth stages after consistent swine manure application, to understand the impacts of swine manure amendment rates on soil chemical and enzymatic properties, and to investigate the correlations between soil enzymatic and chemical variables. The experiment was set out in a randomized complete block design with three replicates and five treatments including three swine manure rates (26, 39, and 52 kg P ha(-1), representing low, middle, and high application rates, respectively) and two controls (no-fertilizer and superphosphate at 26 kg P ha(-1)). The results indicated that the grain yield and soil chemical properties were significantly improved with the application of P-based swine manure from 0 to 39 kg P ha(-1); however, the differences between the 39 (M-39) and 52 kg P ha(-1) treatments (M-52) were not significant. The enzymatic property analysis indicated that acid phosphomonoesterase was the predominant phosphomonoesterase in the tested soil. The M-39 and M-52 treatments had relatively high initial velocity (V-0), maximal velocity (V-max), and activation grade (lgN(a)) but low Michaelis constant (K-m), temperature coefficient (Q(10)), activation energy (E-a), and activation enthalpy (Delta H), implying that the M-39 and M-52 treatments could stimulate the enzyme-catalyzed reactions more easily than all other treatments. The correlation analysis showed that the distribution of soil phosphomonoesterase activities mainly followed the distributions of total C and total N. Based on these results, 39 kg P ha(-1) could be recommended as the most appropriate rate of swine manure amendment.Soil phosphomonoesterase plays a critical role in controlling phosphorus (P) cycling for crop nutrition, especially in P-deficient soils. A 6-year field experiment was conducted to evaluate soil phosphomonoesterase activities, kinetics and thermodynamics during rice growth stages after consistent swine manure application, to understand the impacts of swine manure amendment rates on soil chemical and enzymatic properties, and to investigate the correlations between soil enzymatic and chemical variables. The experiment was set out in a randomized complete block design with three replicates and five treatments including three swine manure rates (26, 39, and 52 kg P ha(-1), representing low, middle, and high application rates, respectively) and two controls (no-fertilizer and superphosphate at 26 kg P ha(-1)). The results indicated that the grain yield and soil chemical properties were significantly improved with the application of P-based swine manure from 0 to 39 kg P ha(-1); however, the differences between the 39 (M-39) and 52 kg P ha(-1) treatments (M-52) were not significant. The enzymatic property analysis indicated that acid phosphomonoesterase was the predominant phosphomonoesterase in the tested soil. The M-39 and M-52 treatments had relatively high initial velocity (V-0), maximal velocity (V-max), and activation grade (lgN(a)) but low Michaelis constant (K-m), temperature coefficient (Q(10)), activation energy (E-a), and activation enthalpy (Delta H), implying that the M-39 and M-52 treatments could stimulate the enzyme-catalyzed reactions more easily than all other treatments. The correlation analysis showed that the distribution of soil phosphomonoesterase activities mainly followed the distributions of total C and total N. Based on these results, 39 kg P ha(-1) could be recommended as the most appropriate rate of swine manure amendment