Concrete Calculator: Pour Planner & Strength Gain

Concrete volume and supply

For slabs and rectangular footings, $V=LWh$. Circular columns use $V=\pi D^2H/4$. A solid staircase is the sum of $n$ stacked tread prisms: $V=Wa r\,n(n+1)/2$. Multiply by the number of identical elements. Add the user allowance, then independently round ready-mix up to the supplier's increment or bags up to whole bags. Delivery count uses the rounded ready-mix order. QUIKRETE training, attached s2 page 11, supplies the 0.60 ft³ and 0.45 ft³ bag yields. The rounding subtraction of $10^{-10}$ removes floating-point noise at exact integer boundaries.

Rectangular reinforcement takeoff

The supplied cover is clear cover to the outside of the steel. The outer bar centre spans are $L-2c-d$ and $W-2c-d$. Bars parallel to L number $\lceil(W-2c-d)/p\rceil+1$, with at least two; interchange L and W for the other direction. Equal spacing fits between the boundary bars. Straight cut lengths are $L-2c$ and $W-2c$. Multiply by mats and identical elements. Theoretical mass uses $\rho\pi d^2/4$ with nominal steel density 7850 kg/m³. These geometry and mass equations are derived here, not a reinforcement design rule.

Temperature and strength

Use the constant-concrete-temperature Arrhenius equivalent-age method described by FHWA-HIF-07-004 (attached s1 pages 2–3), with the fib Model Code 2010 benchmark $Q=E_a/R=4000\,K$: $a_T=\exp[Q(1/293.15-1/T_K)]$, $t_e=a_T t$. This normalises the reference precisely to 20 °C using 273.15 rather than the rounded 273 and 13.65 constants. It uses the fib benchmark, not FHWA's alternative temperature-dependent activation-energy correlation.

The EN 1992-1-1:2004, clause 3.1.2 / fib Model Code 2010 development function is $f_{cm}(t_e)=f_{cm,28}\exp[s(1-\sqrt{28/t_e})]$. CEM I benchmarks are s = 0.20 (42.5 R, 52.5 N/R), 0.25 (32.5 R, 42.5 N), and 0.38 (32.5 N), as reported in Vollpracht et al. 2018, attached s3 page 4; equivalent-age basis is on page 24. This planner withholds results below one equivalent day and caps the ratio at 1 above 28 equivalent days. For a target fraction $r=f_{target}/f_{cm,28}$, inverse age is $t_{e,target}=28/[1-\ln(r)/s]^2$; divide by $a_T$ for calendar days.

One uniform shape per run; repeated elements are identical. Slabs and footings are rectangular prisms, columns are solid circles, and steps have a solid underside, equal treads/rises and no landing. Concrete volume does not subtract reinforcement displacement. The default 10% concrete and 5% steel allowances are editable planning choices, not standard requirements.

Bag yield defaults refer to the cited product; they do not specify its strength coefficient. The entered mean 28-day strength and strength targets must share the same test basis. Characteristic design strength must not be substituted for mean strength without justification. Moisture remains sufficient for hydration. Concrete temperature is uniform and constant throughout the curing period; air temperature is only a rough proxy when verified to be representative.

A rectangular grid mat contains two crossing bar sets. Mat fit checks cover geometric occupancy only. Steel purchasing allowance is not a splice design or a stock-bar cutting schedule. Defaults for form release (15 MPa) and vehicle access (25 MPa) are illustrative user targets, not universal requirements.

Quantity planning and educational strength estimates only. Nominal CEM I concrete, entered mean strength 10–60 MPa, average concrete temperature 5–35 °C, calendar horizon 1–56 days, and strength-model equivalent age 1–28 days. The source study specifically cautions against predictions before 24 equivalent hours (s3 page 5). Curves contain intentional gaps below this limit; beyond 28 equivalent days they plateau at the entered reference strength. Blended binders, retarders, accelerators and unfamiliar mixes need test-calibrated parameters; changing s alone does not calibrate temperature sensitivity.

The constant-temperature forecast is not an ASTM C1074 calibrated field maturity assessment. It omits hydration heat, temperature history, moisture loss, freezing, consolidation defects and early-temperature effects on ultimate strength. FHWA requires mix-specific calibration and verification (s1 pages 2–4). Form removal, shoring changes and vehicle loading require approval by the responsible engineer using appropriate in-place strength evidence and capacity/load checks. Reaching a target in this forecast is not permission to strip forms or drive on concrete. Continue curing according to the project requirements and supplier instructions. Check against the standard in force and local project specifications; the cited strength-development formulation follows the stated older edition, not an assertion of compliance with EN 1992-1-1:2023.