ASTM C140 is the standard test method that laboratories use to sample and evaluate concrete masonry units before they go into walls, foundations, and retaining structures. Formally titled C140/C140M, it lays out how to measure a unit’s dimensions, compressive strength, absorption, density, moisture content, and, for certain product types, flexural load and ballast weight.1ASTM International. Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units When an inspector or engineer asks whether your blocks “meet C140,” they are asking to see lab reports proving the units passed these tests against the limits set by a companion specification.
What ASTM C140 Covers
C140 applies to standard hollow concrete masonry units used in load-bearing walls, segmental retaining wall units, articulating concrete blocks used for erosion control, paving units, and manufactured concrete ballast units. Not every test in the standard applies to every product; the annexes break out procedures by category.
C140 is the exam, not the rulebook. The pass/fail limits come from separate specifications: ASTM C90 sets performance requirements for load-bearing concrete masonry units, and ASTM C129 covers non-load-bearing units used in interior partitions and infill walls. A C140 report tells you what the units measured; the applicable specification tells you whether those numbers are good enough.
How Sampling Works
Accurate results start with pulling the right number of specimens from the production lot. For lots of 10,000 units or fewer, six units are selected. Lots between 10,000 and 100,000 units require twelve. For lots above 100,000, six units are pulled from every 50,000-unit portion. The purchaser can always request more.
Of the six units in a standard sample, three go to compression testing and three to absorption and density evaluation.2ASTM International. ASTM C140/C140M-22 – Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units Each specimen carries a unique identifier from the production facility or job site through every stage of lab work, along with its date of manufacture and the production line that made it.
Dimensional Measurements
Lab personnel use calipers or steel rules to measure each unit’s width, height, and length at multiple points, then average the readings. Face shell thickness and web thickness are recorded separately because those dimensions determine the net cross-sectional area, which is the figure used in every strength calculation that follows.
Those same measurements feed the volume used to calculate density. A volume error propagates: it throws off the density figure, the weight classification, the absorption limit that applies, and the structural assumptions built on top of all three.
Absorption, Density, and Moisture Content
Absorption testing measures how much water a unit will take on, which affects durability in freeze-thaw climates and long-term resistance to moisture damage. Specimens are weighed in several states: as-received, fully immersed, saturated surface-dry, and oven-dry.
Units are immersed in water for 24 to 28 hours before saturated weights are recorded. They then go into a ventilated oven set at 230°F (plus or minus 9 degrees) for at least 24 hours. The oven-dry weight is not final until two consecutive weighings taken two hours apart show the unit is losing no more than 0.2 percent of its weight between readings. Cutting this step short is the most common source of inaccurate absorption data.
The difference between saturated and oven-dry weight, divided by the unit’s volume, gives the absorption rate. Under ASTM C90, the maximum average absorption for three units depends on the weight classification:
- Lightweight units: 18 lb/ft³
- Medium-weight units: 15 lb/ft³
- Normal-weight units: 13 lb/ft³
Density is calculated from the oven-dry weight and the measured volume, and it determines which of those three weight classifications applies. Moisture content at delivery is derived by comparing the as-received weight to the oven-dry weight.
Compressive Strength Testing
Compressive strength is the headline number. The specimen goes into a calibrated hydraulic press and is loaded until it fails; the peak force divided by the net cross-sectional area gives the strength in pounds per square inch.
Before the press touches the unit, both bearing surfaces must be capped so contact is flat and even. ASTM C1552 governs capping and typically calls for high-strength gypsum or sulfur compounds to fill surface irregularities.3ASTM International. Standard Practice for Capping Concrete Masonry Units, Related Units and Masonry Prisms for Compression Testing Cap thickness cannot exceed ⅛ inch. A poor cap concentrates load unevenly and can crack a sound unit prematurely.
Loading happens in two phases. The press applies force up to roughly half the expected breaking load at any convenient rate. The second half must then be applied over no less than one minute and no more than two minutes, which prevents the shock loading that would skew results.
For load-bearing units under ASTM C90, the minimum average net-area compressive strength is 2,000 psi.4ASTM International. Recent Changes to ASTM Specification C90 and Impact on Concrete Masonry Units A batch that falls short is typically rejected, and the manufacturer has to look at its mix design, curing, or equipment before resubmitting.
Who Can Perform C140 Testing
Not every facility is equipped to run C140. ASTM C1093 sets the baseline for testing agencies, covering personnel qualifications, equipment calibration, facility standards, and quality management.5ASTM International. Standard Practice for Accreditation of Testing Agencies for Unit Masonry
The Cement and Concrete Reference Laboratory (CCRL), a joint program of ASTM International and the National Institute of Standards and Technology, conducts on-site inspections of masonry labs. Inspectors check compression machines, ovens, capping equipment, measurement tools, and balances, and a technician demonstrates the sampling, dimensional measurement, capping, compression, and absorption procedures while the inspector observes.6CCRL. Laboratory Inspection Program Descriptions CCRL’s role is advisory rather than formal accreditation, but its inspection reports carry weight with specifiers.
For formal accreditation, many jurisdictions look for AASHTO accreditation, which requires the lab’s quality management system to meet the AASHTO Accreditation Procedure Manual and AASHTO R 18. Maintaining it means regular assessments, participation in proficiency sample programs, and resolving any identified problems within 60 days.7AASHTO re:source. AASHTO Accreditation Overview
The Test Report and Building Code Compliance
The report is the legal proof that units on the project meet spec. It must include the test date, the manufacturer’s name, the source of the samples, and results for compressive strength, absorption, and oven-dry density. Building inspectors review these before allowing construction to proceed.
The International Building Code ties into this through its special inspection requirements. Under IBC Chapter 17, materials must be approved in writing after satisfactory completion of required tests and submission of test reports. The building official keeps each approval on file, and those records must be available for public review.8ICC Digital Codes. Chapter 17 Special Inspections and Tests The code also requires that the testing agency be independent of the contractor, keep equipment properly calibrated, and employ qualified staff.
When results come back below minimums, the consequences move quickly. Building departments can withhold certificates of occupancy, and penalties for inaccurate or incomplete documentation vary by jurisdiction. The practical cost is usually schedule: sourcing and retesting replacement material takes weeks, and catching the failure after the blocks are already in the wall is far more expensive than catching it in the lab.