Concrete Mix & Placing Spec Finder
Enter site conditions to derive the maximum coarse aggregate size, slump, air content, water-binder ratio limit, and curing period under KCS 14 20 10 — with the governing clause shown alongside.
Result
Max. coarse aggregate size
25mm
Governed by Table 2.2-5 standard value
- Table 2.2-5 standard
- 25 mm
- Also allowed by the table
- 20 mm
- Slump (Table 2.2-6)
- 80~150 mm
- Air content (Table 2.2-7)
- 4.5 %
- Allowed range after delivery
- 3~6 %
- Max. water-binder ratio — Durability rule 1.9 (4)
- ≤ 60 %
- Moist curing period (Table 3.4-1)
- 5 days
- Max. interval between lifts (Table 3.3-1)
- 2.5 h
- Max. free-fall height at placing
- ≤ 1.5 m
- Total chloride ion in fresh concrete
- ≤ 0.3 kg/m³
- Water-soluble chloride ion in hardened concrete (28 days, % of cement mass)
- ≤ 0.3 %
- Min. specified strength required
- —
- Required average strength f_cr
- 32.5 MPa
Standard deviation unknown or 14 or fewer tests — Table 2.2-2
- f_ck + 8.5
- 32.5 MPa
Up to 0.60 kg/m³ with engineer approval and corrosion-protection measures.
Source: KCS 14 20 10 Normal Concrete (under KCS 14 20 00 Concrete Works Standard Specification, notified by MOLIT, Korea)
Test standards: slump KS F 2402 · slump flow KS F 2594 · air content KS F 2409, KS F 2421 · specimens KS F 2403 · compressive strength KS F 2405 · water-soluble chloride KS F 2713, KS F 2715
Actual mix proportions must be determined by testing; this result is for checking specification standard values.
What this tool does
The concrete mix and placing spec finder takes your site conditions and returns, on one screen, the maximum coarse aggregate size, standard slump, entrained air content, water-binder ratio limit, moist curing period, and allowed interval between lifts as set out in KCS 14 20 10 (Normal Concrete), the Korean standard specification notified by the Ministry of Land, Infrastructure and Transport. Unlike quantity calculators that answer 'how much material do I need', this tool answers 'which specification is standard under these conditions'. The important part is that it does not simply look values up in a table — it resolves the competition between clauses. The maximum coarse aggregate size is bounded not only by the standard value in Table 2.2-5 (20 or 25 mm for the general case, 40 mm for large sections and plain concrete), but also by four dimensional limits at the same time: one fifth of the minimum clear distance between form faces, one third of the slab thickness, three quarters of the minimum clear spacing between bars, bundled bars, tendons or ducts, and — for plain concrete — one quarter of the minimum member dimension. If any one of these falls below the tabulated standard, that clause governs the final size. Missing this competition and ordering purely from the table value is a common cause of segregation and poor consolidation after placing. The water-binder ratio behaves the same way: the durability rule caps it at 60 %, but de-icing chemicals tighten it to 45 %, a watertightness requirement to 50 %, and carbonation resistance to 55 %, and when several conditions overlap the strictest one applies. On top of that sit Table 2.2-3 (special exposure) and Table 2.2-4 (sulfate exposure); where both must be considered, the specification requires the stricter of the two (note 1 to Table 2.2-3), so the smaller water-binder ratio and the larger minimum specified strength apply. The strictest case of all is concrete exposed to — or sprayed with — de-icing chemicals, salt, brackish water or seawater for rebar corrosion protection, which demands a water-binder ratio of 0.40 and at least 35 MPa. The required average strength f_cr is derived here too: the applicable equations split at a specified strength of 35 MPa, both equations in each range are evaluated and the larger governs, and the standard deviation is multiplied by the Table 2.2-1 correction factor for 29 or fewer tests, or replaced by the Table 2.2-2 addition when there are 14 or fewer tests or no records at all. This tool shows the governing clause next to each result, so the basis can be explained directly to the supervisor or client. Because a reduced aggregate size also changes the standard air content in Table 2.2-7, the two are derived together, and the moist curing period follows Table 3.4-1 by cement type and daily mean temperature — below 5 ℃ it tells you to move to the cold-weather concrete standard instead of extrapolating.
Who uses this
- Reviewing mix conditions before placing — standard aggregate size, slump, and air content
- Checking in advance whether member dimensions pull the aggregate size below the tabulated value
- Fixing the water-binder ratio limit when de-icing, watertightness, and carbonation conditions overlap
- Deriving the moist curing period from cement type and ambient temperature
- Reviewing the ready-mix designation (max aggregate size – nominal strength – slump) before ordering
- Deriving the required average strength f_cr from test-record standard deviation, or from Table 2.2-2 when no records exist
- Checking the minimum specified strength demanded by special and sulfate exposure classes
- Answering supervision comments with the specific specification table behind each value
How to use
- 1Select whether the concrete is reinforced or plain and whether the section is general or large. These two choices fix the row and column in Tables 2.2-5 and 2.2-6.
- 2Enter only the dimensions you know among form clearance, slab thickness, bar clear spacing, and minimum member dimension. Leaving a field at 0 excludes it from the limits.
- 3Set the freeze-thaw exposure and tick de-icing chemicals, watertightness, or carbonation as applicable — the air content and water-binder limit update immediately.
- 4Enter the cement type and daily mean temperature to get the moist curing period and the allowed interval between lifts.
- 5Read the governing clause shown under the result to see which provision produced the value.
Rules applied
Max coarse aggregate size = largest standard size not exceeding min(Table 2.2-5 value, dimensional limit) dimensional limit = min(form clearance × 1/5, slab thickness × 1/3, bar clear spacing × 3/4, min member dimension × 1/4) standard sizes: 10, 15, 20, 25, 40 (mm) Standard slump (Table 2.2-6, mm) Reinforced general 80–150 / large section 60–120 Plain general 50–150 / large section 50–100 Standard air content (Table 2.2-7, %) — tolerance after delivery ±1.5 % Max size (mm) 10 15 20 25 40 Severe 7.5 7.0 6.0 6.0 5.5 Moderate 6.0 5.5 5.0 4.5 4.5 Water-binder ratio limit = min(applicable conditions) durability 60 % / de-icing chemicals 45 % / watertightness 50 % / carbonation 55 % Moist curing period (Table 3.4-1, days) Daily mean temp Ordinary Portland Slag / fly ash type B High-early-strength 15 ℃ or above 5 7 3 10 ℃ or above 7 9 4 5 ℃ or above 9 12 5 Allowed interval between lifts (Table 3.3-1) — above 25 ℃ 2.0 h, at or below 25 ℃ 2.5 h Required average strength f_cr (2.2.2) — larger of the two equations in each range f_ck ≤ 35 MPa (2.2-1) f_cr = f_ck + 1.34s (2.2-2) f_cr = (f_ck − 3.5) + 2.33s f_ck > 35 MPa (2.2-3) f_cr = f_ck + 1.34s (2.2-4) f_cr = 0.9 f_ck + 2.33s s = standard deviation of compressive strength (MPa) Table 2.2-1 correction factor (29 or fewer tests) 15 tests 1.16 · 20 tests 1.08 · 25 tests 1.03 · 30+ tests 1.00 (interpolate linearly) Table 2.2-2 for 14 or fewer tests, or no records f_ck below 21 → f_ck+7 · 21–35 → f_ck+8.5 · above 35 → f_ck+10 Table 2.2-3 special exposure — max water-binder ratio / min specified strength Exposed to water, low permeability required 0.50 / 27 MPa Freeze-thaw or de-icing chemicals in moist state 0.45 / 30 MPa Exposed to or sprayed with de-icing chemicals, salt, brackish water or seawater (corrosion) 0.40 / 35 MPa Table 2.2-4 sulfate exposure — SO₄ in soil / SO₄ in water / W-B / min f_ck Negligible 0.0–0.1 % 0–150 ppm — — Moderate 0.1–0.2 % 150–1,500 ppm 0.50 27 MPa Severe 0.2–2.0 % 1,500–10,000 ppm 0.45 30 MPa Very severe above 2.0 % above 10,000 ppm 0.45 30 MPa * Where Tables 2.2-3 and 2.2-4 both apply, follow the stricter (note 1 to Table 2.2-3)
Worked examples
Example 1: general reinforced column, 40 mm clear bar spacing
The Table 2.2-5 standard is 25 mm, and three quarters of the 40 mm clear spacing gives a 30 mm limit. The largest standard size not exceeding 30 mm is 25 mm, so the result stays at 25 mm and Table 2.2-5 governs. If the clear spacing narrows to 20 mm, the limit drops to 15 mm and the spacing clause takes over.
Example 2: 60 mm thick slab
One third of the slab thickness gives a 20 mm limit, which overrides the 25 mm standard. The maximum coarse aggregate size becomes 20 mm, and the air content is then read from the 20 mm row (5.0 % for moderate exposure) rather than the 25 mm row (4.5 %).
Example 3: bridge deck exposed to de-icing chemicals
The water-binder ratio is governed by the 45 % de-icing clause rather than the 60 % durability rule. Even if watertightness (50 %) and carbonation (55 %) also apply, the strictest 45 % stands. The exposure is treated as severe, so a higher air content applies as well.
Example 4: daily mean temperature 8 ℃, blast-furnace slag cement
This falls in the 5 ℃ to below 10 ℃ band of Table 3.4-1, giving a 12-day moist curing period. Under the same conditions ordinary Portland requires 9 days and high-early-strength 5 days — more than a twofold difference by cement type.
Frequently asked questions
Why does Table 2.2-5 say '20 or 25'?
For the general case the specification allows either value. This tool takes the upper bound of 25 mm as the standard and shows 20 mm alongside it. Where reinforcement is congested or consolidation is difficult, 20 mm is the safer choice.
Is the result wrong if I leave the dimension fields empty?
Not wrong, but incomplete. Fields left at 0 are excluded from the limits, so you simply get the Table 2.2-5 standard value. In practice form spacing or bar clear spacing often pulls that value down, so enter whatever the drawings give you.
Why does the air content change with aggregate size?
The smaller the coarse aggregate, the higher the mortar fraction for the same volume, and the more entrained air is needed for freeze-thaw resistance. That is why Table 2.2-7 steps the values down from 10 mm to 40 mm.
Why is there no result below a daily mean temperature of 5 ℃?
Table 3.4-1 only applies at 5 ℃ and above. Below that, the separate cold-weather concrete standard (KCS 14 20 40) applies, so the tool points you there rather than extrapolating values of its own.
Why take the larger of the two equations for the required average strength?
Because the specification says so. For f_ck up to 35 MPa, both Eq. (2.2-1) f_ck + 1.34s and Eq. (2.2-2) (f_ck − 3.5) + 2.33s are evaluated and the larger becomes the required average strength. The first limits the average shortfall probability, the second limits results falling well below the specified strength — both must be satisfied, so the larger governs. A small standard deviation tends to let the first equation govern; a large one, the second.
Why does it ask for the number of strength tests?
Because how far the standard deviation can be trusted depends on it. With 30 or more tests the calculated standard deviation is used as is; with 15–29 it is multiplied by the Table 2.2-1 factor (1.16 at 15, 1.08 at 20, 1.03 at 25). With 14 or fewer tests, or no records, the Table 2.2-2 additions (f_ck+7 / +8.5 / +10) replace the standard deviation entirely. Counts not listed are interpolated linearly.
What happens if I select both a special exposure and a sulfate exposure?
Note 1 to Table 2.2-3 requires following the stricter of the two tables. This tool applies the smaller water-binder ratio and the larger minimum specified strength, and shows which table governed.
Can I batch concrete directly from these values?
No. The specification requires the actual mix to be established by testing. These values are for quickly checking the standard values and limits the specification sets; the final mix must follow the mix design, test results, and the approval of the responsible engineer and supervisor.
Cautions
- •These results are for checking the standard values and limits in KCS 14 20 10. The actual mix must be established through mix design and testing.
- •If you leave the dimension fields empty you only get the Table 2.2-5 standard value. Enter the form clearance and bar spacing your drawings give you.
- •The aggregate size limits may be waived at the judgement of the responsible engineer where a compaction method that fills without voids is used (proviso to 2.2 (1)).
- •A daily mean temperature below 5 ℃ falls under cold-weather concrete (KCS 14 20 40), and marine structures under KCS 14 20 44 — separate standards apply.
- •The required average strength depends heavily on how reliable the standard deviation is. Without test records it falls back to Table 2.2-2 — recompute once real test data exists.
- •If the specified strength falls below what the exposure class (Tables 2.2-3 and 2.2-4) requires, no mix adjustment fixes it — the strength must be raised at the design stage.
- •Specifications are revised over time. Check the current edition at the Korea Construction Standards Center (kcsc.re.kr) before ordering.
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Last reviewed: 2026-09-08