Material for cement hydration - CemhydMat

CemhydMat represents a hydrating material based on CEMHYD3D model version 3.0, developed at NIST [5]. The model represents a digital hydrating microstructure, driven with cellular automata rules and combined with cement chemistry. Ordinary Portland cement is treated without any difficulties, blended cements are usually decomposed into hydrating Portland contribution and intert secondary cementitious material. The microstructure size can be from to over  m. For standard computations the size suffices.

Each material instance creates an independent microstructure. It is also possible to enforce having different microstructures in each integration point. The hydrating model is coupled with temperature and averaging over shared elements within one material instance occurs during the solution. Such approach allows domain partitioning to many CemhydMat instances, depending on expected accuracy or computational speed. A more detailed description with engineering examples was published [25]. Tab. 56 summarizes input parameters.


Table 56: Cemhydmat - summary.
Description Cemhyd - hydrating material
Record Format CemhydMat num(in) # d(rn) # k(rn) # c(rn) # file(s) # [eachGP(in) #] [densityType(in) #] [conductivityType(in) #] [capacityType(in) #] [castingtime(rn) #] [nowarnings(ia) #] [scaling(ra) #] [reinforcementDegree(rn) #]
Parameters - num material model number
  - d material density
  - k Conductivity
  - c Specific heat capacity
  - file XML input file for cement microstructure and concrete composition
  - eachGP 0 (default) no separate microstructures in each GP, 1 assign separate microstructures to each GP
  - densityType 0 (default) get density from OOFEM input file, 1 get it from XML input file
  - conductivityType 0 (default) get constant conductivity from OOFEM input file, 1 compute as [21]
  - capacityType 0 (default) get capacity, 1 according to Bentz, 2 according to XML and CEMHYD3D routines
  - castingtime optional casting time of concrete, from which hydration takes place. Absolute time is used.
  - nowarnings supresses warnings when material data are out of standard ranges. The array of size 4 represent entries for density, conductivity, capacity, temperature. Nonzero values mean supression.
  - scaling components in the array scale density, conductivity, capacity in this order. nowarnings are checked before scaling.
  - reinforcementDegree specifies the area fraction of reinforcement. Typical values is 0.015. Steel reinforcement slightly increases concrete conductivity and slightly decreases its capacity. Thermal properties of steel are considered 20 W/m/K and 500 J/kg/K.
Supported modes _2dHeat, _3dHeat


The input XML file specifies the details about cement and concrete composition. It is possible to start all simulations from the scratch, i.e. with the reconstruction of digital microstructure. Alternatively, the digital microstructure can be provided directly in two files; one for chemical phases, the second for particle's IDs. The XML input file can be created with the CemPy package, obtainable from http://mech.fsv.cvut.cz/smilauer/index.php?id=software. The CemPy package alleviates tedious preparation of particle size distribution etc.

The linear solver (specified as NonStationaryProblem) performs well when the time integration step is small enough (order of minutes) and heat capacity, conductivity and density remain constant. If not so, use of nonlinear solver is strongly suggested (specified as NlTransientTransportProblem).

Borek Patzak
2018-01-02