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Cement Versus Concrete

Cement versus Concrete

Scraping a chalkboard (also known as a blackboard) with fingernails produces a sound and feeling most people find extremely irritating. Basis of this innate reaction to sound has been studied in the field of psychoacoustics (branch of psychology concerned with perception of sound and its physiological effects).

mr owl tootsie roll popIn response to audio stimuli, a human mind’s way of interpreting sound can be translated through a regulatory process called Reticular Activating System. Located in the brain stem, the Reticular Activating System continually listens, even throughout delta-wave sleep, to determine importance of sounds in relation to waking cortex or rest of body from sleep. Chalkboard scraping, or noises illiciting an emotional response, have been known to trigger tendencies from the fight or flight response acting as the bodys primary self-defense mechanism.

Superman has his Kryptonite, mine happens to be misused construction terms. Here, in Middle America, I have gradually adapted to term “rafters” being used for roof trusses. My favorite chalkboard scrape happens to be with use of “cement” when the correct term would be “concrete”.

Although terms cement and concrete often are used interchangeably, cement is actually an ingredient of concrete. Concrete is a mixture of aggregates and paste. Aggregates are sand and gravel or crushed stone; paste is water and portland cement.

Cement comprises from 10 to 15 percent of concrete mix, by volume. Through a process called hydration, cement and water harden and bind aggregates into a rocklike mass. This hardening process continues for years meaning concrete gets stronger as it gets older.

Portland cement isn’t a brand name, but a generic term for a cement type used in virtually all concrete, just as stainless is a type of steel and sterling a type of silver. Therefore, there is no such thing as a cement sidewalk, or a cement mixer; proper terms are concrete sidewalk and concrete mixer. I rest my case.


CLSM: Cost Effective Alternative to Soil Backfill

Backfilled HoleIn typical pole building construction, holes are augured into the earth, columns are placed in the hole so concrete can be placed below the column to act as a footing for vertical support, as well as to encase the lower portion of the column. Above this “bottom collar” compacted soil backfill is used to fill the void between the column and the edges of the holes.

Controlled low-strength material (CLSM) is self-compacted, cementitious material primarily used as a structural fill or backfill alternative to compacted soil backfill. It is often referred to by different names including flowable fill, controlled density fill, soil-cement slurry, unshrinkable fill, plastic soil cement and flowable mortar. It is self-leveling, having the approximate consistency of pancake batter, and can be placed in one lift with minimal labor and no vibration or tamping. The American Concrete Institute (ACI) defines CLSM as having a compressive strength less than 1200 psi (pounds per square inch), however most current CLSM applications require unconfined compressive strengths of less than 300 psi. This lower strength is more than comparable with strength of compacted soil backfill.

Since CLSM is designed to be fluid, it can be easily placed as backfill in a hole. Soil backfill, even if compacted properly in the required layer thicknesses, cannot achieve the uniformity and density of CLSM.

CLSM mixtures typically consist of water, portland cement, fly ash, and fine or course aggregates, or both. Some mixtures contain only water, portland cement, and fly ash. Although the materials used in CLSM may meet ASTM or other standard specifications, it is often not necessary to use standardized materials. The selection of materials for use in CLSM is based on cost, specific CLSM application and the required mixture characteristics including flowability, strength, excavatability and density. The use of fly ash improves the CLSM flowability, and can also increase strength and reduce the mixture’s bleeding, shrinkage and permeability. Air-entraining admixtures are also often used to help improve workability, reduce bleeding, help minimize segregation, reduce the unit weight, and control strength development.

Aggregates are usually the major component in CLSM, and their type, grading and shape can affect physical properties. Unlike conventional concrete aggregate, which is usually required to meet standardized specifications, CLSM aggregate need not necessarily meet these same standards to be effective. As an example, manufactured sands containing up to 20% non-deleterious dust of fracture have proven to be very satisfactory