Astm D 1557

[Marine Farinha]

TheProctor Compaction Test establishes the maximum unit weight that a particular type of soil can be compacted to using a controlled compactive force at an optimum water content. This is the most common laboratory soil test and the basis for all engineered compacted soil placements for embankments, pavements, and structural fills. In-place measured densities of the compacted fill are compared to the Proctor test results to determine the degree of soil density.

Soils are the most basic and least expensive construction materials available. For all of human history, construction projects from primitive burial mounds to modern interstate highways have removed, replaced, filled, or shaped the soil surface to accommodate pavements and structures or to make the earthwork itself a structure. Experience and experimentation have taught us that compacting the soils we place makes the installation more permanent, along with some other advantages.

In the latter part of World War ll and later into the 1950s, heavier dynamic loads from larger aircraft and heavier, more frequent truck traffic were placing greater demand on pavements and soil subgrades. Sometimes the compacted soils had passing density tests based on standard Proctor values but were still deflecting too much under load to carry the increased forces. In simple terms, densities were too low, and optimum moistures were too high for these increased loadings. At the same time, field compaction equipment was becoming larger and more efficient, making it possible to compact soils to higher densities at lower moisture contents. The modified Proctor test was introduced in 1958 as ASTM D1557 and AASHTO T 180 to help with these applications at higher loads.

Test procedures are similar, but the laboratory compactive effort of the modified method is higher. Using a 10lb (4.54kg) hammer with 18in (457.2mm) free-fall instead of the 5.5lb (2.49kg) hammer with 12in (304.9mm) drop. This results in higher maximum soil densities at lower optimum moisture contents. The modified Proctor is used today concurrently with the standard Proctor. The selection of the method is based on project requirements and specifications. This blog post will focus on the significance of soil compaction (particularly the Proctor Test), how the test is performed, the necessary equipment, and helpful tips.

NOTE: There are variations of test procedures noted in both the standard and modified test methods that are dictated by the maximum particle sizes of the soil samples. The variations affect the preparation of the samples, test practices, and the type of equipment required. The reader is encouraged to carefully read and understand the ASTM or AASHTO test methods.

A representative bulk field sample is obtained for each type of soil material proposed for use in the earthwork operation. Weights required for the bulk sample will range from about 50lb to 100lb (23kg to 45kg) of the moist sample, depending on the test method specified. Back in the lab, processing of the samples begins with gradual air-drying to the desired moisture, usually around 10% or more below the anticipated optimum moisture. For cohesive soils, this can be expedited by breaking down clumps and spreading the sample out on open trays.

Once the soil is friable enough, the breakdown can continue more thoroughly. It is important to read and understand your particular test method carefully, as there are several variables that can affect this stage of sample preparation. For most standard and modified Proctor variations, this means reducing the finer materials to pass through either a 4.75mm (#4) or a 9.5mm (3/8in) sieve. Coarser materials are set aside for particle size determinations and, in some cases, for adding proportionally back into the final test specimens. At this stage, sample breakdown and coarse particle sizing are often performed concurrently.

NOTE: This article serves as an informational guide to equipment and techniques used to perform the Proctor moisture/density relationship tests as described in ASTM D698 and D1557 or AASHTO T 99 or T 180 test methods. The information contained herein is in no way intended to supersede the specifications or test protocol of these published test methods.

For each Proctor point, the operator compacts the specimen into the pre-weighed soil compaction mold assembly in three to five layers (lifts) according to the method required. The manual soil compaction hammers are lifted to their maximum height and allowed to fall freely onto the soil specimen for the required number of blows. For standard Proctors, the hammers weigh 5.5lb (2.5kg) and drop 12in (305mm). The modified Proctor method uses a 10lb hammer with 18in (457mm) drop height for compaction. Automatic/mechanical compactors are also available to make this process easier. After compaction, the collar is removed, and excess soil is carefully trimmed with a straightedge tool, so the compacted soil is flush with the top of the mold. Small voids can be manually filled with excess samples. The mold with the sample is then weighed and recorded, and the soil is extruded from the mold. A sample of the specimen is obtained to determine the exact moisture content by oven drying, and the process is repeated for subsequent samples.

The moist density, or unit weight, of each compacted specimen is computed by dividing the mass of the soil (minus the mold assembly) by the volume of the mold. To find the dry density, divide the moist density by the percent moisture divided by 100, plus 1.

The results are plotted on a graph as dry unit weight vs. moisture content and will show the curvilinear relationship that allows the maximum dry weight and optimum moisture for each type of soil to be established.

The saturation curve, or zero air voids curve, is a plot of soil density vs moisture at a theoretical 100% saturation level (zero air voids). Points for plotting the curve are calculated from compacted dry unit weights of the sample material adjusted to moisture contents at 100% saturation, using this formula stated in the ASTM D698 standard test method, among others:

The saturation curve serves as a guide when plotting dry unit weights on the soil compaction curve. The wet side of the compaction curve should roughly parallel the saturation curve. In theory, if the two curves intersect, there has been an error in testing, calculating, or plotting the results.

When performing a field density test, the dry unit weight is compared to the maximum dry weight of the Proctor tests to calculate a percent of compaction. When the required densities are hard to reach in the field, the moisture content should be compared to the optimum moisture content from the lab tests. If field moistures differ more than 2% or 3%, it becomes more difficult to compact to the required density. Field moisture can be adjusted by aerating/discing the soil or by adding water.

ALEXANDRIA, Va., Dec. 17, 2020 /PRNewswire/ -- CSI and global standards organization ASTM International finalized an agreement to formally link CSI's UNIFORMAT standards and ASTM International's E1557 (UNIFORMAT II) standards within CROSSWALK , a gated web service of the CSI-owned Construction Information Network, LLC (CIN), a platform which seamlessly integrates CSI classifications into construction technology platforms and data flows.

UNIFORMAT is CSI's U.S. and Canadian standard for classifying building specifications, cost estimating, and cost analysis used to provide consistency in the economic evaluation of building projects. The ASTM International E1557 standard, managed by ASTM's performance of buildings committee (E06), expands descriptions of many existing elements. Integrating these two classification standards in CROSSWALK enables the Architecture, Engineering, Construction and Owners (AECO) industry to easily communicate and build with the utmost accuracy, safety and cost-effectiveness.

By connecting UNIFORMAT and ASTM E1557 via CROSSWALK, architects, engineers, BIM managers, contractors and cost estimators will be able to translate between the two standards seamlessly in software applications that take advantage of CROSSWALK." said Mark Dorsey, CEO of CSI.

"With this integration, we are seeking to solve the problem users of UNIFORMAT and ASTM E1557 have traditionally faced when determining which standard to use," said Brian Meincke, VP of Global Business Development and Innovation at ASTM International. "Our agreement with CSI greatly improves the quality of construction information and communication among various users of the tool. This integration furthers our commitment to providing our vast user base with the most accurate and up-to-date information needed to deliver the highest quality of work," Meincke added.

Launched in May 2020 by CIN, CROSSWALK is a first-in-class digital classification engine for the AECO community. This tool augments the design and construction process by enabling construction technology platforms to connect through an Application Programming Interface (API). The API connects to and curates' versions of CSI's construction information classifications and standards that span decades. ASTM E1557 standards will now be included among these versions. For more about CROSSWALK, visit www.crosswalk.biz.

About CSIThe Construction Specifications Institute, Inc. is a national association of more than 7,000 members dedicated to improving the communication of construction information by continuously developing and transforming standards and formats, education, and certification. Visit www.csiresources.org for more information.

The Proctor compaction test is a laboratory method of experimentally determining the optimal moisture content at which a given soil type will become most dense and achieve its maximum dry density. The test is named in honor of Ralph Roscoe Proctor [de], who in 1933 showed that the dry density of a soil for a given compactive effort depends on the amount of water the soil contains during soil compaction.[1] His original test is most commonly referred to as the standard Proctor compaction test; his test was later updated to create the modified Proctor compaction test.

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