ACI Strength Testing Cheat Sheet

Cheat sheet ACI Strength Testing Cheat Sheet Practice Questions Study Guide Print / Save PDF

ASTM C39 Compressive Strength Not published of exam Loading Rate Fracture Types L/D Correction Cylinder Tolerances

ASTM C78 Flexural Strength Not published of exam Third-Point Loading Modulus of Rupture Span Geometry Fracture Location

ASTM C617 Sulfur Capping Not published of exam Cap Thickness Hardening Time Capping Plate Sulfur Safety

ASTM C1231 Unbonded Caps Not published of exam Shore A Durometer Retainer Ring Pad Reuse Limits Pad Inspection

Lab Practice & Program Info Not published of exam C1077 Accreditation ACI 318 Acceptance Machine Verification Exam Logistics

Quick Facts Exam CSTT (ACI) Credential Concrete Strength Testing Tech Written Qs ~40 MC, min 8/standard Time 1 hr written + performance Pass 70% overall, 60% each Format Written + hands-on demo Level Lab technician Workbook CP-19, 25th Edition Validity 5 years

C39 Fracture Types 1-6 AS Cone, Cone+Crack, Column, Diagonal, Side, Point 1: double cone 2: one cone 3: columnar 4: diagonal 5/6: side/point

C39 vs C78 Testing AS

C39 Compressive Cylinders P/A formula 10 psi report

C78 Flexural Beams PL/bd² formula 5 psi report Cylinder crush vs beam bend

C39 Fracture Type Diagnosis AS Cones on both ends → Type 1 ( Normal, well-capped ) One cone plus cap cracks → Type 2 ( Minor cap issue ) Columnar cracks both ends → Type 3 ( Check capping quality ) Diagonal, no end cracks → Type 4 ( Tap to confirm ) Side break at top/bottom → Type 5 ( Common with unbonded ) Pointed side break → Type 6 ( Check pad and alignment )

C39 Loading Rate & Reporting AS Loading rate 35 ± 7 psi/s Rate range 28 to 42 psi/s Strength report Nearest 10 psi Specimen age From water/cement add 28-day tolerance ± 20 hours 7-day tolerance ± 6 hours 3-day tolerance ± 2 hours 24-hour tolerance ± 0.5 hour

Fracture Type 1 vs Type 3 AS

Type 1 Cones both ends Normal failure

Type 3 Columnar cracks Capping problem Good cap vs bad cap

C39 Specimen Tolerances AS End planeness 0.002 in maximum Perpendicularity 0.5°, ~1/8 in./12 in. Diameter measure Nearest 0.01 in. Length measure Nearest 0.05 diameter Minimum L/D 1.00 ratio L/D above 1.75 No correction applied Aggregate rule Diameter ≥ 3× max agg

C39 L/D Correction Factors AS L/D 1.75 Factor 0.98 L/D 1.50 Factor 0.96 L/D 1.25 Factor 0.93 L/D 1.00 Factor 0.87 L/D > 1.75 No factor needed

C39 Fracture Types AS Type 1 Cones both ends Normal Type 2 One cone plus cracks Type 3 Columnar cracks, no cone Type 4 Diagonal shear fracture Type 5 Side break, top/bottom Type 6 Pointed side break

C39 Machine Requirements AS Load accuracy ± 1.0% of load Verify frequency Annual + after repair Bearing block size ≥ 3% over diameter Platen planeness 0.001 in. in 6 in. Verified range floor ≥ 10% of capacity Spherical seat lube Petroleum-type oil only

Middle-Third vs Outside-Third Formula AS

Middle third R = PL/bd² Most common case

Outside third, ≤5% R = 3Pa/bd² Use distance a Fracture location sets formula

Which C78 Formula To Apply AS Fracture in middle third → R = PL / bd² ( Standard case ) Fracture under 5% outside → R = 3Pa / bd² ( a = to nearest support ) Fracture over 5% outside → Discard the result ( Invalid test ) Before loading a beam → Verify span 3× depth ( Within 2% tolerance )

C78 Modulus of Rupture Formulas AS Middle-third fracture R = PL / bd² Outside-third fracture R = 3Pa / bd² Discard rule > 5% outside middle third Rupture report Nearest 5 psi

C78 Geometry & Loading Rate AS Span-to-depth 3× depth, ± 2% Stress rate 125-175 psi/min Standard beam 6 x 6 x 21 in. Dimension measurement At fractured section Measurement precision Nearest 0.05 in. Load pattern Third-point loading

C617 Hardening Times AS Low strength 2 hours, high strength 16 hours Under 5000 psi: 2 hr 5000 psi+: 16 hr Never skip the check

C617 vs C1231 Capping AS

C617 Sulfur Bonded mortar 2-16 hr harden 1/4 in. thick

C1231 Unbonded Neoprene pad Reusable instantly 1/2 in. pad Bonded mortar vs reusable pad

Which Capping Method To Use AS Strength 1,500-12,000 psi → Unbonded neoprene cap ( ASTM C1231 ) Strength outside that range → Sulfur or ground ends ( Not C1231 eligible ) Ends not plane 0.002 in. → Cap, grind, or saw ( Before testing ) One end already sulfur-capped → Unbonded cap other end ( Mixed capping OK ) High-volume acceptance testing → Unbonded pads ( Faster turnaround ) Need highest cap strength → Sulfur mortar ( 16 hr for 5000 psi+ )

C617 Cap Dimensions AS Cap thickness avg 1/4 in. (6 mm) Cap thickness max 5/16 in. (8 mm) Cap planeness 0.002 in., same as C39 Plate oversize ≥ 1 in. over diameter Plate planeness 0.002 in. in 6 in.

C617 Process & Safety AS Sulfur temperature About 265°F (130°C) Hardening, under 5000 psi 2 hours minimum Hardening, 5000 psi+ 16 hours minimum Cap strength at 2 hr 5,000 psi minimum Compound reuse limit 5 uses before recharge Reuse at 5000 psi+ Not permitted Hazard gas Hydrogen sulfide (H2S) End condition needed Must be dry first

C1231 Durometer Matching AS Softer pad for low strength, firmer pad for high strength 50 duro: 1500-6000 psi 60 duro: 2500-7000 psi 70 duro: highest strength

Shore A 50 vs 60 Pads AS

Shore A 50 1,500-6,000 psi Softer pad

Shore A 60 2,500-7,000 psi Firmer pad Match durometer to strength

C1231 Pad & Ring Specs AS Pad thickness 1/2 in ±1/16 in Durometer tolerance ± 5 points Retainer inside diameter 102-107% of specimen Retainer cavity depth ≥ 2× pad thickness Pad reuse limit 100 uses (unqualified) Crack discard rule > 3/8 in. length

C1231 Durometer vs Strength AS Shore A 50 1,500-6,000 psi Shore A 60 2,500-7,000 psi Usable strength range 1,500-12,000 psi Below 1,500 psi Unbonded caps barred Above 12,000 psi Unbonded caps barred

CSTT Pass Rule GE Seventy overall, sixty each standard, both exams required 70% overall 60% per standard Written + performance

Written vs Performance Exam GE

Written exam 40 MC questions 1 hour, closed-book

Performance exam Hands-on demo Pass/fail only Both required to certify

Which ASTM Standard Applies GE Cylinder compressive break → ASTM C39 ( Load / area ) Beam flexural break → ASTM C78 ( Modulus of rupture ) Sulfur mortar capping → ASTM C617 ( Bonded caps ) Neoprene pad capping → ASTM C1231 ( Unbonded caps ) Lab accreditation rules → ASTM C1077 ( Personnel + equipment )

Lab Practice & Program Facts GE Lab accreditation standard ASTM C1077 Personnel requirement CSTT certification One strength test Average of 2 cylinders Low-test trigger > 500 psi below f'c 3-test average rule Average must reach f'c Certification validity 5 years from passing Written exam pass 70% overall, 60% each Written exam length 40 MC, 1 hour

Standards Tested (Editions) GE C39/C39M-18 Compressive strength cylinders C78/C78M-18 Flexural strength beams C617/C617M-15 Sulfur mortar capping C1231/C1231M-15 Unbonded neoprene caps

Common Traps

L/D correction ≠ always applied Only if L/D ≤ 1.75 ≠ Above 1.75, no correction

C39 age ≠ demold time Age counts from water add ≠ Not from demolding time

Cap thickness avg ≠ max Average 1/4 in. allowed ≠ Max 5/16 in. any point

Type 5/6 ≠ automatic fail Common with unbonded caps ≠ Investigate pad condition first

70% overall ≠ enough alone Also need 60% per standard ≠ Both criteria must pass

Written exam ≠ whole cert Performance exam required too ≠ Both parts must pass

Pad hardness ≠ fixed value ± 5 point tolerance allowed ≠ Check hardness annually

Last Minute 1 . C39 rate: 35±7 psi/s 2 . C39 report: nearest 10 psi 3 . C78 report: nearest 5 psi 4 . C78 span: 3× depth 5 . C617 caps: 1/4 in. avg 6 . C617 harden: 2 or 16 hr 7 . C1231 pad: 1/2 in. thick 8 . C1231 durometer: ± 5 tolerance 9 . Pass rule: 70% plus 60% each 10 . Both exams required to certify 11 . L/D correction only below 1.75 12 . End planeness: 0.002 in. max

ACI Concrete Strength Testing Technician Practice Questions 100 questions Study Guide 21 topics Cheat Sheet 78 facts Flashcards 50 cards Blogs 1 blog Free CE Podcast

Third-party resources · We may earn a commission from purchases.

Concrete Strength Testing Technician Certification-An Illustrated Guide for ACI Certification By Ullikashi, Pradeep $40.00 · Buy on Amazon

Same family resources Explore More ACI Concrete Certifications Continue into nearby exams from the same family. Each card keeps practice questions, study guides, flashcards, videos, and articles in one place.

ACI Concrete Field Testing Technician Grade I Cheat Sheet 70 facts Practice Questions 100 questions Study Guide 72 topics Flashcards 50 cards Videos 1 video Blogs 2 blogs 1 Job Wiki Free CE

ACI Aggregate Testing Technician Level 1 Practice Questions 108 questions Study Guide 22 topics Free CE

ACI Tilt-Up Supervisor Practice Questions 117 questions Blogs 1 blog Free CE

ACI Adhesive Anchor Inspector Practice Questions 100 questions Free CE

ACI Adhesive Anchor Installer Practice Questions 100 questions Free CE

ACI Aggregate Testing Technician Level 2 Practice Questions 100 questions Free CE

More From This Family Videos and articles for deeper review. Video ACI Field Testing Grade I Exam Guide 2026: FREE Study Plan Article ACI Concrete Strength Testing Technician Exam Guide 2026 9 min read Article ACI Field Testing Grade I Exam Guide 2026: FREE Study Plan 28 min read Article ACI Grade 1 Performance Exam Workflow: Sequence, Handoffs, and Recovery 12 min read Article FREE ACI Tilt-Up Supervisor Exam Guide 2026: Requirements, Study Plan, and Practice 9 min read

Independent exam preparation notice OpenExamPrep is an independent education provider, not affiliated with or endorsed by the exam sponsors named on this site. Exam and certification names identify what our resources help you study for; they do not imply sponsorship, approval, or review of our materials. Unless a resource expressly identifies authorized public material, our practice questions are independently developed simulations, not actual, recalled, or sponsor-provided exam items. We aim to reflect publicly available exam outlines and topic information in our study resources. Coverage, format, and difficulty may differ from the actual exam, and we cannot guarantee that every detail is accurate or current. Confirm exam requirements, fees, and policies with the official exam sponsor. Updated 2026-07-17 . Official exam sources checked CP-19, 25th Edition (2022) . This is a study aid only and is not for use during the exam. ACI Concrete Strength Testing Technician (official) CP-19 25th Edition Technician Workbook (ACI Store) ASTM C39/C39M Standard Test Method ASTM C78/C78M Standard Test Method