# 027 — Cure Line

## Problem Situation

Concrete looks hard within hours of pouring. But actual structural strength depends on accumulated temperature and time — the maturity index. Cold weather slows hydration invisibly; freezing stops it entirely. Hot weather accelerates it but risks thermal cracking. Contractors need to know when it's safe to strip formwork, apply loads, or open to traffic, but the concrete's actual strength state is invisible.

Current workarounds: fixed-time rules ("wait 3 days"), which ignore temperature entirely; cylinder break tests, which measure a separate specimen in a lab (not the actual pour); or experience-based guessing. The Nurse-Saul maturity method exists as a mathematical model but is locked in lookup tables and spreadsheets — the curve itself is never seen.

## What Was Built

A maturity accumulation instrument. A canvas-rendered strength curve shows estimated percent of 28-day design strength rising over time, driven by an hourly temperature profile. Threshold lines mark critical milestones: strip vertical forms (25%), strip slab forms (50%), apply full load (75%), and design strength (100%). A temperature strip below the curve shows the hourly temperature profile as a color-coded bar.

Four presets demonstrate dramatically different curing scenarios: Summer Pour (28/20°C, fast curing), Mild Autumn (15/8°C, moderate), Cold Weather (5/−2°C, slow with some freezing hours), and Freeze Risk (2/−8°C, nearly stalled — 68 of 96 hours below freezing). Adjustable design strength (25-40 MPa). Hover to scrub through the timeline and read maturity index, temperature, and estimated strength at any hour.

A comparison strip at the bottom shows all four scenarios at the 48-hour mark side by side — compressing the key insight that identical concrete reaches vastly different strengths depending on temperature history.

## Why This Form

The Nurse-Saul maturity function is an integral — the area under the temperature-time curve above a datum temperature. The accumulation curve IS the mathematical structure of the problem. A rising curve with threshold lines is the native representation of "invisible state approaching a safe point." Tables give numbers; this gives trajectory.

## What Is Actually Interesting Here

The dramatic contrast between presets reveals what fixed-time rules hide. Summer Pour reaches 47% at 48 hours; Freeze Risk reaches only 15%. A contractor following a "strip at 48 hours" rule would be safe in summer but structurally dangerous in cold weather. The freeze-risk curve's near-flatness during nighttime hours (when temperature drops below the datum) makes the stop-start nature of hydration viscerally legible — each freezing night is a dead zone where maturity accumulates nothing.

The temperature strip below the curve creates a causal link: you can see the temperature oscillation and immediately read its effect on the strength curve's slope. Warm hours = steep curve. Cold hours = flat curve. Below freezing = zero contribution.

## Iterations

None. The first version captured the core move cleanly.

## Next Step

Add a "what-if blanket" interaction: toggle insulated curing blankets that raise nighttime temperatures by 8-12°C, and watch the maturity curve shift earlier. This would make the instrument actionable — showing the economic value of temperature protection in hours saved.

## Art Direction Note

Dark editorial direction. Canvas-rendered curve with restrained warm amber palette for the strength curve and threshold markers. Blue tint in the temperature strip for cold/freezing hours. Geist for interface text, JetBrains Mono for labels and data. Generous negative space. Minimal chrome.

## Promotion Candidate Read

Maybe. The form-to-problem fit is native — the maturity integral IS the curve. The preset contrast genuinely reveals something invisible (same concrete, vastly different strength trajectories). But the instrument is diagnostic-only with preset temperature profiles. Needs real temperature input (manual hourly entry or sensor integration) and the blanket what-if interaction to graduate from educational to operationally useful.
