1. Overview & Quick-Start Guide

• Draw a Box or Custom Polygon: Use Draw Box or enter exact $W \times H$ dimensions in $\text{mm}$, or click Draw Custom Shape to draw arbitrary 2D cross-sections (L-walls, sloped walls, foundations).
• Alter Corners & Sides: Drag corner handles (C1, C2, ...) directly on the canvas, use Move Entire Side to push/pull any wall, or click + Add Corner on Side to split a wall at its midpoint.
• Configure Each Wall Independently: Click any wall of the cross-section to assign its thermal boundary (plywood, insulated formwork, steel formwork, open air, rock/existing concrete), formwork stripping time ($t_{\text{strip}}$), wind speed ($v$), and mechanical restraint (free, fixed, roller, or elastic spring stiffness).

2. Concrete Maturity & Arrhenius Equivalent Age ($t_e$)

Mathematical Formulation (Freiesleben Hansen & Pedersen, 1977)

The activation energy $E_a(T)$ $[\text{J/mol}]$ is constant at temperatures $\ge 20^\circ\text{C}$ and increases linearly below $20^\circ\text{C}$ down to $-10^\circ\text{C}$:

Arrhenius affinity rate factor $H(T)$ relative to $20^\circ\text{C}$ ($293.15\text{ K}$) and equivalent age increment $\Delta t_e$ $[\text{hours}]$:

where $R = 8.31446\text{ J/(mol}\cdot\text{K)}$ is the universal gas constant and $k_{Ea} \approx 1470\text{ J/(mol}\cdot\text{K)}$.

3. Hydration Heat Generation & 2D Transient Heat Conduction

Degree of Hydration $\alpha(t_e)$ and Volumetric Heat Rate $\dot{q}_{\text{hyd}}$

where $\tau$ $[\text{hours}]$ is the hydration time constant, $\beta$ $[-]$ is the shape parameter, and $Q_{\text{pot}}$ $[\text{J/kg}]$ is the potential heat per kg of concrete.

Transient 2D FEM Heat Equation

4. Per-Wall Thermal & Mechanical Boundaries (Formwork, Stripping & Subbase)

Effective Heat Transfer Coefficient $h_{\text{eq}}(t)$ $[\text{W/(m}^2\cdot\text{K)}]$

Standard Formwork & Subbase Presets

5. Stiffness, Tensile Strength, Creep & Crack Risk (EN 1992-1-1 / Eurocode 2)

Property Evolution per Eurocode 2 ($t_d = t_e / 24\text{ days}$)

Creep Relaxation (Trost-Bažant AAEM) & Incremental Stress Analysis

• $u < 0.70$ (Green): Safe (low crack risk).
• $0.70 \le u < 1.00$ (Yellow): Elevated crack risk warning.
• $u \ge 1.00$ (Red): Tensile stress exceeds tensile strength ($\sigma_1 \ge f_{ctm}$) — cracking expected.

6. Known Engineering Simplifications & Modeling Assumptions in V1

1. Linear-Elastic Pre-Cracking Stress ($u = \sigma_1 / f_{ctm}$): The utilization ratio $u = \sigma_1 / f_{ctm}(t_e)$ identifies when and where tensile strength is exceeded ($u \ge 1.0$). Once $u > 1.0$, the solver reports the uncracked linear-elastic utilization ratio rather than softening element stiffness or computing discrete crack opening widths ($w_k$).
2. Incremental AAEM Creep vs. Full Kelvin-Maxwell Chain: Early-age viscoelastic relaxation is modeled via the incremental Age-Adjusted Effective Modulus ($E_{\text{eff}}$), plastic setting threshold ($\alpha_0 = 0.12$), and early heating relaxation rather than a multi-unit Kelvin chain memory integral. For standard 3–7 day thermal assessments, this achieves close agreement with much faster solve times.
3. 1D Boundary Ground Contact vs. Full 2D Soil/Base Block: In V1 single-box mode, contact with ground or existing concrete is represented via boundary conductance $h_{\text{ground}}$ and spring stiffness $(k_x, k_y)$. Full 2D heat diffusion into an underlying foundation slab will be modeled directly once Multi-Box Staged Casting is enabled in Phase 2.