HYDCEM: a New Cement Hydration Model

Hydration models are useful to predict, understand and describe the behaviour of different cementitious-based systems. They are indispensable for undertaking long-term performance and service life predictions for existing and new products for generating quantitative data in the move towards more sustainable cements while optimising natural resources. One such application is the development of cement-based thermoelectric applications. HYDCEM is a new model to predict the phase assemblage, degree of hydration, heat release and changes in pore solution chemistry over time for cements undergoing hydration for any w/c ratio and curing temperatures up to 450C. HYDCEM, written in MATLAB, is aimed at complementing more sophisticated thermodynamic models to predict these properties over time using user-customisable inputs. A number of functions based on up to date cement hydration behaviour from the literature are hard-wired into the code along with user-changeable inputs such as the cement chemical (oxide) composition, cement phase densities, element molar mass, phase and product densities and heat of hydration enthalpies. HYDCEM uses this input to predict the cement phase and gypsum proportions, volume stoichiometries and dissolution and growth of hydration products from the silicates, aluminates and ferrites, including C-S-H, calcium hydroxide, hydrogarnet (if applicable) ettringite and monosulphate. A number of comparisons are made with published experimental and thermodynamic model results and HYDCEM predictions to assess its accuracy and usefulness. The results show that HYDCEM can reasonably accurately predict phase assemblages in terms of volume change and behaviour for a range of cements and curing temperatures. It is proposed that HYCEM can complement more sophisticated thermodynamic models to give users a reasonable prediction of cement behaviour over time

Thermodynamic Cement Hydration Modelling Using HYDCEM

Thermodynamics have been successfully applied to the field of cement hydration science to predict the formation of phase assemblages and pore solution chemistry. For any cement hydration model to be accepted, it must provide accurate forecasts of which solids may form and how the cement will dissolve over time. This is particularly important for the ongoing development of new sustainable cements and understanding their hydration behaviour in service. HYDCEM is a cement hydration model that simulates volumetric changes of cement and gypsum dissolution and product growth that, up to now, assumed which solids would form. In order to improve its usefulness, the PHREEQC geochemical software has been coupled with HYDCEM to provide more sophisticated and flexible predictions of which phases may form under equilibrium conditions and generate their change in volume over time for curing temperatures between 5-45°C, variable w/c ratio and cement oxide compositions. To incorporate the coupling of PHREEQC into the model, HYDCEM was re-written in the C# programming language (previously coded in MATLAB) which also improved overall performance and functionality. This paper presents analysis of a cement system with a w/c ratio of 0.5 at a curing temperature of 20°C and provides predictions of the phase assemblage, phase and product changes in volume and heat evolution over a 1,000-day period in one hour time-steps

Why, What, and How of Rigour and Relevance in Management Research

In his 1993 presidential address to the assembled faithful of the Academy of Management Don Hambrick posed the question, “What if the academy actually mattered” (1994:11). This rhetorical question set his esteemed colleagues, world leading management scholars, in the category of perhaps rigorous knowledge workers, but definitely not relevant to their community of practice. One might presume that when Hambrick, a giant of his era with a record of citations that is the envy of most scholars, and a field of work (upper echelons) that has been defined by his contribution for over 20 years, we would take note and act. Unfortunately three years later Richard Mowday (1997:341) found it necessary to return to the theme in his presidential address referring to what has ultimately become a perennial challenge of being both rigorous and relevant. In 2002 Jean Bartunek (2003:203) had a dream for the academy where we work to make a difference and speak to tensions involving theory and practice. In 2005 Denise Rousseau (2006) addressed the topic through the search for evidence based management to bridge the research-practice divide. We look forward with anticipation to the new challenges evoked in this years speech, but hardly expect an announcement that we have risen to the challenge. The European debate on the issue has had equal longevity and coverage, with the British Academy of Management leading a search in 1995 for the academic beast that could leap Pettigrew’s (2001) double hurdle. What emerged was a debate closely aligned with the call for a transition from Mode 1 to Mode 2 forms of enquiry (Gibbons et al., 1994; Nowotny et al., 2001) most notably characterised by Tranfield and Starkey (1998) who argued that management research must take account of the fields ontology as a discipline of practice which aligns it more with engineering than pure science and lends itself to Mode 2 collaborative enquiry. Despite diversions towards Mode 1.5 (Huff, 2000) recognising that Mode 1 and Mode 2 are not dichotic, the call for a move to Mode 2 was carried through to the influential Starkey-Madan report (2001), albeit with the caution that it was not Mode 2 at the expense of Mode 1. We were then offered the tantalising thought of moving to Mode 3 (Starkey, 2001)! Despite the attention brought to the issue by such eminent scholars the conversation has stubbornly remained in this conceptual phase. Perhaps because we are too wedded to our traditional approaches or perhaps we have not found the means of articulating the method needed to match our emerging theory. One attempt to move the theory towards a method of investigation is provided by McLean, MacIntosh and Grant (2002) with the first comprehensive articulation of the five key features of mode 2 enquiry in what they call their 5mode2 framework and it is from this point that we try to take up the challege to transcend Mode 1 in our teaching and research. Whether we have reached mode 1.5, Mode 2, Mode 3, Hodgkinson’s Pragmatic Science (2001:S42) or Pettigrew’s double hurdle (2001) is unclear. The intention of our paper is not to propose a neatly packaged Mode 1.75 approach or a lofty Mode 4, but rather it is to explore the struggle, reaffirm the need, and point to the opportunities. The paper is structured around three key issues. First, the question of why so little progress has been made in the intervening period? Second, we question what is considered to be managerially relevant research and who gets to decide together with the allied question of what we consider to be rigour and how this is evolving ? Third we discuss the challenges for the future. A later version of this paper was published in the Irish Journal of Management and the full text is available here http://eprints.maynoothuniversity.ie/7924

Simulating cement hydration using HYDCEM

HYDCEM is a new cement hydration model to simulate volumetric changes and predict phase assemblage, degree of hydration, heat release, compressive strength and chemical shrinkage over time for PC and limestone binders undergoing hydration for any w/c ratio and curing temperatures between 5 and 45 °C. While models should never completely remove experimental analysis, they are an aid to better understand cement hydration and microstructure development by allowing users analyse different binders in a relatively short time. HYDCEM, written in MATLAB®, is aimed at complementing more sophisticated thermodynamic models giving users a reasonable prediction of hydration behaviour over time, using user-customisable inputs. A number of functions based on up to date cement hydration behaviour from the literature are included along with user-changeable inputs such as the cement chemical (oxide) composition, cement phase densities, species molar mass, phase and product densities and heat of hydration enthalpies. HYDCEM uses this input to predict the cement phase and gypsum proportions, volume stoichiometries and growth of hydration products including C-S-H, calcium hydroxide, hydrogarnet (if applicable), hydrotalcite, ettringite, monosulphate, hemicarbonate and monocarbonate if limestone is present. A number of comparisons with published experimental and thermodynamic model results and HYDCEM predictions are provided to demonstrate its accuracy and usefulness. Previous work has shown that HYDCEM can reasonably accurately predict phase assemblages in terms of volume change and behaviour for a range of cements and curing temperatures

Spreading Leader Knowledge: Investigating a Participatory Mode of Knowledge Dissemination among Management Undergraduates

In this paper we discuss the need for a practitioner–academic partnership in disseminating leader knowledge among undergraduate management students, and find that in order to cultivate actionable skill development, business and academic communities should collaborate to offer a participatory approach to leadership education. The core objective is to discover sources of actionable knowledge and to decipher its optimum dissemination among management students, encompassing technical, conceptual and human kill development, through interaction with both theory and practice, in order to prepare students for active participation, and potential leadership, in the business environment. Based on a comprehensive literature review, we propose a participatory leader knowledge dissemination model, where business leaders can stimulate the academic environment, and leadership skill development can be promoted through practitioners’ active involvement in the education process. The article concludes with a perspective on the evolution of knowledge transfer among management students and the current trend towards dynamic collaboration between academics and corporate leaders

Modelling the Addition of Limestone in Cement using HYDCEM

Hydration models can aid in the prediction, understanding and description of hydration behaviour over time as the move towards more sustainable cements continues. HYDCEM is a new model to predict the phase assemblage, degree of hydration and heat release over time for cements undergoing hydration for any w/c ratio and curing temperatures up to 450C. HYDCEM, written in MATLAB, complements more sophisticated thermodynamic models by predicting these properties over time using user-friendly inputs within one code. A number of functions and methods based on up to date cement hydration behaviour from the literature are hard-wired into the code along with user-changeable inputs including w/c ratio, curing temperature, chemical compositions, densities and enthalpies. Predictions of hydration product volumes from the silicate, aluminate and ferrite phases can be determined, including C-S-H, calcium hydroxide, hydrogarnet (if applicable) ettringite and monosulfate. A number of comparisons have been made with published phase assemblages using thermodynamic models and HYDCEM predictions to assess its accuracy and usefulness. This paper presents simulations of cement hydration and microstructure development with and without the additional of ground limestone using the HYDCEM model, both in terms of monocarbonate growth at the expense of monosulfate and ettringite. Comparisons with published phase assemblages show good agreement in terms of volumetric growth and behaviour

Thermodynamic Modelling of Harsh Environments on the Solid Phase Assemblage of Hydrating Cements Using PHREEQC

Poor durability of reinforced concrete structures can lead to serious structural failures. An accurate model to observe the effects of aggressive agents like carbonation, sulfate ingress, and seawater solutions on the solid phase assemblagewill help designers and specifiers better understand howcement behaves in these environments. This paper presents the first steps in developing such a model using the PHREEQC geochemical software by accounting for alkali binding and dissolution. It also presents the use of discrete solid phases (DSPs) to account for the solid-solution behaviour of siliceous hydrogarnet and magnesium silicate hydrate (M-S-H). A new thermodynamic description of the vaterite phase has also been developed for this work using the cemdata18 thermodynamic database. The predicted phase assemblages of cements in these environments here agree with previously published findings using a different thermodynamic model supported with experimental data

Employing Discrete Solid Phases to Represent C-S-H Solid Solutions in the Cemdata07 Thermodynamic Database to Model Cement Hydration Using the PHREEQC Geochemical Software

This paper presents a cement hydration model over time using the cemdata07 thermodynamic database and a series of derived discrete solid phases (DSPs) to represent calcium silicate hydrate (C-S-H) as a binary solid solution with two end-members. C-S-H in cement is amorphous and poorly crystalline with a range of molar Ca/Si ratios from 0.6 to 1.7. It displays strongly incongruent dissolution behaviour, where the release of calcium into solution is several orders of magnitude greater than silicon. It is, therefore, important that any cement hydration model provides a credible account of this behaviour. C-S-H has been described in the cemdata07 thermodynamic database as a number of solid solutions using different end-members with differing levels of complexity. While solid solutions can be included in most modern geochemical software programs, they often lead to a significant increase in computation time. This paper presents how an incongruent solid solution between two C-S-H end-members may be represented as a number of DSPs to model cement hydration over time using the PHREEQC geochemical software. By using DSPs rather than modelling C-S-H as a nonideal solid solution, this gives the user full control of the input for the model, reducing the computational demand and analysis time with no loss in accuracy in predicting stable-phase assemblages and their associated pore chemistry over time

Predicting Mortar Compressive Strength Using HYDCEM

The compressive strength of mortar is a significant property that will influence its performance in concrete or masonry. Being able to accurately model and predict the mortar compressive strength would be of great benefit to suppliers and end users alike that could possibly reduce the need for multiple physical testing. A section of the original HYDCEM cement hydration model (amoungst others) has been partitioned to focus on predicting the compressive strength of Portland cement and cement-limestone mortars, entitled HYDCEM_CompressiveStrength. The model uses the cement/binder oxide composition along with other inputs to predict the compressive strength development over time. This paper presents a study into how accurately the HYDCEM_CompressiveStrength model can predict the mortar’s compressive strength over time for European cements. Experimental results of mortar cube’s and bar’s compressive strength in accordance with ASTM C 109 for a CEM I + 10% limestone binder and EN196-1 for a CEM I and CEM II cement are presented along with predictions from the model following a parametric study. Comparisons have shown reasonably good agreement between measured and predicted values over time

Deriving discrete solid phases from CSH-3T and CSHQ end-members to model cement hydration in PHREEQC

This paper presents a cement hydration model over time using the CEMDATA thermodynamic database and a series of discrete solid phases (DSP) to represent calcium silicate hydrate (C-S-H) as a ternary (CSH-3T) and quaternary (CSHQ) solid solution. C-S-H in cement is amorphous and poorly crystalline with a range of molar Ca/Si ratios = 0.6-1.7 and displays strongly incongruent dissolution behaviour where the release of calcium into solution is several orders of magnitude greater than silicon. It is therefore important that any cement hydration model provides a credible account of this behaviour. C-S-H has been described in the CEMDATA thermodynamic database as a number of binary, ternary and quaternary solid solutions using different end-members with differing levels of complexity. While solid solutions can be included in most modern geochemical software programs, it often leads to a significant increase in computation time. This paper presents how the two of the more complex C-S-H solid solutions, CSH-3T and CSHQ, available in the CEMDATA database, can be represented by DSP to model cement hydration over time using the PHREEQC geochemical software. By using DSP in place of solid solutions, analysis time is much improved with no loss in accuracy in producing stable phase assemblages and reasonable predictions of pH over time