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ACI Aggregate Level 1 practice questions

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Question 1Aggregate sampling and sample reduction

According to standard practice for sampling freshly mixed concrete, from which portion of the discharge should a sample be taken?

  1. From the final portion of the discharge
  2. From the middle portion of the discharge Correct answer.
  3. From any single portion regardless of position
  4. From the very beginning of the discharge

Explanation

Standard practice requires sampling from the middle portion of the discharge, avoiding the first and last fractions, because these portions are not representative of the whole batch. Taking material from the middle reduces segregation effects and yields a sample that reflects the true mixture.

Question 2Aggregate sampling and sample reduction

When a composite sample is required for testing fresh concrete, what is the minimum number of portions that should normally be combined?

  1. Three portions Correct answer.
  2. Two portions
  3. Four portions
  4. Six portions

Explanation

A composite sample is normally formed by combining at least three separate portions taken at different points in the discharge. Combining multiple portions averages out within-batch variation so the composite better represents the whole load.

Question 3Aggregate sampling and sample reduction

What is the standard minimum size for a sample of fresh concrete taken for strength test specimens?

  1. About 20 L Correct answer.
  2. About 50 L
  3. About 5 L
  4. About 10 L

Explanation

A sample for strength specimens should be at least about 20 L (roughly 1 cubic foot) so that enough material is available to mold the required specimens plus reserve. Smaller volumes risk running short and are less representative.

Question 4Aggregate sampling and sample reduction

Why should a sample of fresh concrete be remixed before reducing it?

  1. To restore uniformity lost during sampling and transport Correct answer.
  2. To accelerate the set of the concrete
  3. To increase the air content
  4. To lower the water-cement ratio

Explanation

Transport and handling can cause segregation, so the sample must be remixed to restore uniformity before any reduction or testing. Remixing ensures the reduced portion is representative of the whole sample.

Question 5Aggregate sampling and sample reduction

Which method is appropriate for reducing a large sample of fresh concrete to a smaller test portion?

  1. Dry sieving the sample
  2. Wet sieving or remixing and dividing Correct answer.
  3. Quartering the wet sample
  4. Allowing the sample to set and then crushing it

Explanation

Fresh concrete is reduced by remixing and dividing (or by wet sieving when a mortar sample is needed), which keeps the reduced portion representative. Quartering and dry sieving are aggregate-sample techniques, not fresh-concrete reduction methods.

Question 6Aggregate sampling and sample reduction

A sample of aggregate delivered to the laboratory is to be reduced for testing. Which device is specifically designed for mechanical sample reduction of aggregate?

  1. A riffle splitter Correct answer.
  2. A Vicat apparatus
  3. A slump cone
  4. A flow table

Explanation

A riffle splitter divides a dry aggregate sample into two representative halves by passing it through alternating chutes. It is the standard mechanical device for reducing aggregate samples.

Question 7Aggregate sampling and sample reduction

Which of the following best describes the purpose of sample reduction in aggregate testing?

  1. To remove oversized particles from the sample
  2. To obtain a smaller portion that is representative of the original sample Correct answer.
  3. To dry the sample before testing
  4. To increase the accuracy of individual test results

Explanation

Sample reduction produces a smaller test portion that still represents the original material. The reduced portion must preserve the same proportions of constituents as the parent sample.

Question 8Aggregate sampling and sample reduction

Which action is required to protect a sample of fresh concrete from moisture loss before testing begins?

  1. Add water periodically
  2. Place it in an open tray
  3. Expose it to wind to speed evaporation
  4. Cover it and keep it out of direct sun Correct answer.

Explanation

Fresh concrete samples must be covered and protected from direct sunlight and wind to prevent evaporation, which would alter the water content and workability. Keeping the sample covered preserves its as-delivered condition.

Question 9Aggregate sampling and sample reduction

An aggregate sample is to be reduced by quartering. After mixing and flattening the sample into a circular pile, what is the next step?

  1. Remove the top half of the pile
  2. Wet the pile and scoop from the center
  3. Divide the pile into three equal parts and keep all three
  4. Divide the pile into four equal quarters with a straightedge and remove two opposite quarters Correct answer.

Explanation

Quartering involves flattening the mixed sample and dividing it into four equal quarters, then discarding two diagonally opposite quarters and retaining the other two. This is repeated as needed until the desired size is reached.

Question 10Aggregate sampling and sample reduction

When using a riffle splitter to reduce a dry aggregate sample, how should the material be introduced?

  1. Placed all at once and shaken through
  2. Poured rapidly into one chute
  3. Poured evenly across the full width of the chutes at a steady rate Correct answer.
  4. Dropped in large lumps onto the center divider

Explanation

Material should be poured evenly across the full width of the riffle chutes at a steady rate so it divides equally between the two receiving pans. Uneven or lumped feeding biases the split.

Question 11Aggregate sampling and sample reduction

A composite sample of fresh concrete is to be formed from a truck mixer. From which locations should the individual portions be taken?

  1. All portions from the middle third of the discharge
  2. All portions from the first third of the discharge
  3. Portions distributed across the discharge, avoiding the first and last fractions Correct answer.
  4. All portions from the final third of the discharge

Explanation

Individual portions should be distributed across the discharge while avoiding the very first and very last fractions, then combined into a composite. This distribution captures the batch's variability and yields a representative composite.

Question 12Aggregate sampling and sample reduction

If a wet-sieved mortar sample is required from fresh concrete, what is the purpose of wet sieving?

  1. To remove coarse aggregate so the mortar fraction can be tested Correct answer.
  2. To determine the setting time of the cement
  3. To measure the total air content
  4. To increase the coarse aggregate content

Explanation

Wet sieving passes the fresh concrete through a sieve to separate the mortar from the coarse aggregate, allowing tests that require only the mortar fraction. The mortar retains the same paste and fine aggregate proportions as the concrete.

Question 13Aggregate sampling and sample reduction

A technician collects a sample of fresh concrete and leaves it uncovered in the sun for 30 minutes before molding specimens. What is the most likely effect on the test results?

  1. Increased workability from warming
  2. No effect because concrete is insensitive to evaporation
  3. Increased air content
  4. Reduced water content and altered workability, biasing results Correct answer.

Explanation

Evaporation and solar heating remove water and change the sample's consistency, so specimens molded from it no longer represent the delivered concrete. The sample should have been covered and protected from sun and wind.

Question 14Aggregate sampling and sample reduction

A large field sample of coarse aggregate must be reduced to a laboratory test size. Which sequence best preserves representativeness?

  1. Reduce by taking the largest particles only
  2. Dry the sample, then reduce it with a riffle splitter or by quartering Correct answer.
  3. Reduce by taking the top layer only
  4. Wet the sample, then scoop from the top

Explanation

Aggregate samples are typically dried to constant mass and then reduced by a riffle splitter or quartering so each reduced portion contains the same particle-size distribution as the parent. Taking only a layer or only large particles biases the result.

Question 15Aggregate sampling and sample reduction

Why must the mass of a reduced aggregate test portion meet a minimum requirement rather than being arbitrarily small?

  1. To satisfy insurance requirements
  2. To keep the sample representative and reduce variability of the test result Correct answer.
  3. To increase the apparent density of the aggregate
  4. To make the sample easier to store

Explanation

Minimum mass requirements ensure the reduced portion contains enough particles to be statistically representative and to limit variability in the test result. Portions that are too small can be dominated by a few individual particles.

Question 16Aggregate sampling and sample reduction

A composite sample is formed from three portions of a concrete truck's discharge. How should the portions be combined?

  1. Keep the portions separate and test only the largest
  2. Combine and remix the portions into one homogeneous composite before reducing Correct answer.
  3. Test each portion separately and average the results
  4. Discard the middle portion and use the outer two

Explanation

The individual portions are combined and thoroughly remixed into a single homogeneous composite, which is then reduced to the required test size. Testing portions separately is a different procedure and does not form a composite.

Question 17Aggregate sampling and sample reduction

What is the primary risk of reducing a fresh concrete sample by scooping material from the surface of a settled container?

  1. The sample will set too quickly
  2. The scoop may be contaminated
  3. The air content will decrease
  4. The surface material may be segregated and not representative Correct answer.

Explanation

Settled fresh concrete can segregate, with bleed water or finer paste rising and coarser particles sinking, so surface material is not representative. Remixing and proper dividing avoid this bias.

Question 18Aggregate sampling and sample reduction

When quartering a dry aggregate sample, how are the quarters handled after the pile is divided?

  1. Retain two opposite quarters and discard the other two Correct answer.
  2. Retain all four quarters
  3. Retain three quarters and discard one
  4. Retain one quarter and discard three

Explanation

Quartering retains two diagonally opposite quarters and discards the other two, then repeats the process on the retained material until the desired mass is reached. Retaining opposite quarters preserves the particle-size distribution.

Question 19Aggregate sampling and sample reduction

A sample of fresh concrete must be transported a short distance to the testing station. Which practice best maintains sample integrity?

  1. Transport in a covered container and remix before testing Correct answer.
  2. Transport in a porous sack
  3. Transport in an open wheelbarrow exposed to wind
  4. Transport after adding water to keep it workable

Explanation

Samples should be transported in a covered, non-absorbent container to prevent moisture loss and contamination, then remixed before testing. This preserves the sample's as-delivered condition.

Question 20Aggregate sampling and sample reduction

A laboratory receives a very large aggregate sample and needs a small portion for a sieve analysis. The technician splits the sample once with a riffle splitter and immediately tests the result. What is the main concern with this approach?

  1. Splitting once always over-reduces the sample
  2. The sample must be wetted before splitting
  3. One split may not adequately reduce variability, so splitting should be repeated as needed Correct answer.
  4. A riffle splitter cannot be used for sieve analysis samples

Explanation

Reduction should continue in successive splits until the required test mass is reached, which progressively reduces variability and improves representativeness. A single split may leave a portion that is larger than needed or not sufficiently homogenized.

Question 21Aggregate sampling and sample reduction

Two technicians sample the same concrete truck. Technician A takes all portions from the middle of the discharge; Technician B distributes portions across the discharge. Which statement best explains why Technician B's composite is preferable?

  1. It guarantees higher strength results
  2. It captures within-load variation, making the composite more representative Correct answer.
  3. It avoids the need to remix the sample
  4. It uses more material, which is always better

Explanation

Distributing portions across the discharge captures variation within the load, so the composite better represents the entire batch. Sampling only the middle misses the systematic differences between early and late discharge material.

Question 22Aggregate sampling and sample reduction

A dry aggregate sample is reduced by quartering, but the technician fails to remix the pile thoroughly before flattening and dividing. What is the most likely consequence?

  1. The test result will be unaffected
  2. The aggregate will absorb more water
  3. The sample mass will increase
  4. The reduced portion may not match the parent gradation Correct answer.

Explanation

Thorough mixing before flattening ensures the quarters are homogeneous; without it, segregation can cause the retained quarters to differ in gradation from the parent sample. This biases subsequent test results.

Question 23Aggregate sampling and sample reduction

A fresh concrete sample is wet-sieved to obtain mortar for a test, but the technician discards the coarse aggregate and then adds water to the mortar to restore workability. Why is this practice incorrect?

  1. Adding water changes the mortar's water-cement ratio and invalidates the test Correct answer.
  2. Wet sieving should never be used for mortar
  3. The coarse aggregate should have been retained in the mortar
  4. Mortar cannot be tested in the fresh state

Explanation

The mortar obtained by wet sieving already has the correct water-cement ratio of the concrete; adding water dilutes it and changes the property being measured. The mortar must be tested as separated, without adjustment.

Question 24Aggregate sampling and sample reduction

A technician must prepare a reduced aggregate sample for a test requiring a specific minimum mass. The parent sample is only slightly larger than the required mass. What is the most appropriate action?

  1. Split the sample repeatedly until it is far below the required mass
  2. Add aggregate from another stockpile to reach the mass
  3. Discard the finer particles to reach the mass
  4. Use the entire parent sample without reduction if it meets the required mass Correct answer.

Explanation

If the parent sample is already close to the required test mass, it may be used without reduction, provided it is homogeneous and meets the minimum mass. Unnecessary splitting could leave too little material, and adding or discarding material biases the sample.

Question 25Aggregate sampling and sample reduction

A composite concrete sample is required, but the truck discharge is nearly complete when the technician arrives. Which approach best preserves the intent of composite sampling?

  1. Abandon sampling because the discharge is nearly complete
  2. Take the available portions across the remaining discharge and note the limitation Correct answer.
  3. Take one large portion from the final discharge and call it a composite
  4. Take all portions from the remaining final discharge

Explanation

The technician should take portions across whatever discharge remains while avoiding the extreme final fraction, and document the sampling limitation. Pretending a single final portion is a composite misrepresents the sample.

Question 26Aggregate sampling and sample reduction

A technician must take a representative sample of coarse aggregate from a stockpile. Which sampling practice gives the most representative field sample?

  1. Collect the sample from the outer surface of the pile only.
  2. Collect the sample from several locations and depths around the stockpile. Correct answer.
  3. Take the sample from the base of the stockpile where the material has settled.
  4. Take the sample from the single point where the belt discharges onto the pile.

Explanation

A representative field sample must capture the full range of particle sizes and moisture conditions in the stockpile. Sampling from several locations and depths avoids segregation bias. Material at the base, surface, or a single discharge point tends to be enriched or depleted in certain sizes.

Question 27Aggregate sampling and sample reduction

A field sample of aggregate is reduced with a mechanical sample splitter. What is the key requirement for the splitter to produce representative reduced portions?

  1. The splitter must be operated at high speed to avoid particle bridging.
  2. The splitter must have an even number of chutes and be fed uniformly across its full width. Correct answer.
  3. The sample must be oven-dried before it is passed through the splitter.
  4. The splitter must be cleaned with solvent between each portion.

Explanation

A sample splitter divides material into representative portions only when the sample is introduced uniformly across the full width of the chutes. An even number of chutes allows alternate portions to be combined. Speed, drying, and solvent cleaning are not the controlling requirement.

Question 28Aggregate sampling and sample reduction

A technician reduces a moist, fine aggregate sample by quartering. After the pile is flattened and divided into quarters, which handling of the quarters preserves representativeness?

  1. Retain one pair of opposite quarters, recombine, and repeat as needed. Correct answer.
  2. Retain the quarter with the most visible coarse particles.
  3. Retain the quarter that happens to be largest in volume.
  4. Retain the quarter nearest the technician's working position.

Explanation

Quartering is unbiased only when opposite quarters are selected and recombined, because opposite quarters are treated as equivalent portions of the mixed pile. Choosing quarters by appearance, size, or position introduces bias. The selected material is then remixed and the process repeated until the required mass remains.

Question 29Aggregate sampling and sample reduction

A composite sample of fresh concrete is required from a stationary mixer. How should the individual portions be obtained to make the composite representative?

  1. Take all portions from the first concrete discharged from the mixer.
  2. Take one large portion from the middle of the discharge.
  3. Take portions at regularly spaced intervals throughout the discharge. Correct answer.
  4. Take portions only after most of the load has been discharged.

Explanation

Concrete can vary through a discharge, so a composite must be built from portions taken at regularly spaced intervals across the entire discharge. This captures variation in the batch. Concentrating portions at the start, middle, or end of the discharge over-represents that portion of the load.

Question 30Aggregate sampling and sample reduction

A technician needs a reduced laboratory portion from a large aggregate sample that contains both fine and coarse particles. The parent sample is dry and free-flowing. Which approach best limits segregation during reduction?

  1. Mix the parent sample thoroughly, then reduce it with a splitter or by quartering, repeating until the required mass remains. Correct answer.
  2. Screen out the coarse particles before reducing, then test only the fine fraction.
  3. Pour the sample slowly from a height onto a flat surface, then scoop from the top.
  4. Reduce the sample by taking small scoops from the same spot in the container.

Explanation

Representative reduction requires the parent sample to be well mixed and then reduced by a method that divides all particle sizes equally, such as splitting or quartering, with repetition until the target mass is reached. Removing a size fraction or scooping from one location biases the result. Pouring from height encourages segregation.

Question 31Moisture content and density determination

In ACI terminology, what does the term "density" of concrete refer to when determined from a hardened specimen?

  1. The ratio of solid volume to total volume expressed as a percentage
  2. The oven-dry mass divided by the saturated mass of the specimen
  3. The mass of cementitious material per cubic meter of fresh mixture
  4. The mass per unit volume of the specimen, including its voids Correct answer.

Explanation

Density is mass per unit volume of the concrete as tested, and for hardened concrete it is computed from the measured mass and measured volume of the specimen, which inherently includes permeable voids. It is not a mixture proportion nor a dimensionless ratio.

Question 32Moisture content and density determination

Which moisture state of an aggregate is defined as saturated with all permeable pores filled with water but with no free water on the surface?

  1. Saturated surface-dry Correct answer.
  2. Air-dry
  3. Wet
  4. Oven-dry

Explanation

The saturated surface-dry condition has all permeable pores filled while the particle surface is dry to the touch. Oven-dry has essentially no pore water, and wet aggregate carries visible free surface moisture.

Question 33Moisture content and density determination

Absorption of a coarse aggregate is computed from which pair of masses?

  1. Oven-dry mass and submerged mass
  2. Total mass and dry mass of the sample after washing
  3. Saturated surface-dry mass and submerged mass
  4. Oven-dry mass and saturated surface-dry mass Correct answer.

Explanation

Absorption is the gain in mass of the oven-dry sample when its permeable pores are filled, expressed as a percentage of the oven-dry mass. It therefore requires the oven-dry mass and the saturated surface-dry mass.

Question 34Moisture content and density determination

A sample of fine aggregate has an oven-dry mass of 480.0 g and a saturated surface-dry mass of 492.0 g. What is the absorption, to the nearest 0.1 percent?

  1. 2.4 percent
  2. 1.2 percent
  3. 2.5 percent Correct answer.
  4. 1.0 percent

Explanation

Absorption equals the difference between saturated surface-dry and oven-dry mass divided by the oven-dry mass, times 100. Here 12.0 g divided by 480.0 g gives 0.025, or 2.5 percent.

Question 35Moisture content and density determination

Total moisture content of an aggregate sample is best described as which of the following?

  1. Water held in permeable pores only, expressed on the dry mass
  2. Water removable by a 24-hour air-drying period, on the total mass
  3. Water on the particle surfaces only, on the saturated surface-dry mass
  4. All water in the sample, both absorbed and free surface moisture, on the dry mass Correct answer.

Explanation

Total moisture includes both absorbed water within permeable pores and free water on the surface, and is conventionally expressed as a percentage of the oven-dry mass. Absorption alone accounts only for the pore water.

Question 36Moisture content and density determination

A coarse aggregate has a total moisture content of 4.2 percent and an absorption of 1.3 percent. What is the free moisture content?

  1. 3.2 percent
  2. 2.9 percent Correct answer.
  3. 5.5 percent
  4. 1.3 percent

Explanation

Free moisture is the total moisture minus the absorption, since absorption represents water that fills pores rather than water available to the mixture. Subtracting 1.3 from 4.2 gives 2.9 percent.

Question 37Moisture content and density determination

Why must batch water be adjusted when aggregate is stockpiled wet rather than in a saturated surface-dry condition?

  1. Because wet aggregate increases the cement requirement of the mixture
  2. Because absorbed water is unavailable and must be replaced separately
  3. Because free water on the aggregate adds to the water already batched Correct answer.
  4. Because wet aggregate reduces the entrained air content of the mixture

Explanation

Free moisture on wet aggregate becomes part of the mixing water, so the batched water must be reduced by that amount to hold the water-cementitious materials ratio. Absorbed water, by contrast, is accounted for through absorption and is not free water.

Question 38Moisture content and density determination

A mixture is designed for 180 kg of water per cubic meter with saturated surface-dry aggregate. The coarse aggregate is batched at 2.0 percent free moisture and totals 1100 kg. How much of the batched water should be reduced, to the nearest kilogram?

  1. 36 kg
  2. 22 kg Correct answer.
  3. 2 kg
  4. 11 kg

Explanation

Free water contributed by the aggregate equals the free moisture fraction times the batch mass, or 0.020 times 1100 kg, which is 22 kg. That quantity is subtracted from the batched water.

Question 39Moisture content and density determination

When determining moisture content by oven drying, what is the standard drying temperature for most aggregate moisture determinations?

  1. 60 plus or minus 5 degrees C
  2. 150 plus or minus 5 degrees C
  3. 110 plus or minus 5 degrees C Correct answer.
  4. 230 plus or minus 5 degrees C

Explanation

Aggregate moisture and absorption determinations dry the sample to constant mass at approximately 110 degrees C, which removes free and absorbed water without decomposing the material. Higher temperatures risk altering some constituents.

Question 40Moisture content and density determination

A sample of moist sand has a total mass of 520.0 g and, after oven drying, a mass of 500.0 g. What is the total moisture content, to the nearest 0.1 percent?

  1. 4.2 percent
  2. 4.0 percent Correct answer.
  3. 3.8 percent
  4. 2.0 percent

Explanation

Moisture content is the mass of water divided by the oven-dry mass, times 100. The water mass is 20.0 g and the dry mass is 500.0 g, giving 4.0 percent.

Question 41Moisture content and density determination

Bulk specific gravity of an aggregate is computed using which volume?

  1. The volume of solids plus permeable pores, excluding the space between particles Correct answer.
  2. The volume of water displaced by the saturated surface-dry sample only
  3. The volume of solids only, excluding all permeable pores
  4. The volume of solids plus permeable pores, including the space between particles for the dry-rodded case

Explanation

Bulk specific gravity is based on the volume of the particles including their permeable pores but excluding the voids between separate particles. This distinguishes it from apparent specific gravity, which excludes permeable pores.

Question 42Moisture content and density determination

Which specific gravity value is numerically the largest for the same aggregate?

  1. Bulk specific gravity on a dry-rodded basis
  2. Bulk specific gravity on a saturated surface-dry basis
  3. Bulk specific gravity on an oven-dry basis
  4. Apparent specific gravity Correct answer.

Explanation

Apparent specific gravity excludes the permeable pores from the volume, giving the smallest denominator and therefore the largest value. Bulk values include those pores and are lower, with the oven-dry basis being the lowest of the bulk values.

Question 43Moisture content and density determination

A coarse aggregate has an oven-dry mass of 1000.0 g, a saturated surface-dry mass of 1018.0 g, and a submerged mass of 635.0 g. What is the bulk specific gravity on an oven-dry basis, to the nearest 0.01?

  1. 2.57
  2. 2.61 Correct answer.
  3. 1.61
  4. 1.57

Explanation

Bulk specific gravity on the oven-dry basis is the oven-dry mass divided by the saturated surface-dry mass minus the submerged mass. Here 1000.0 divided by 383.0 equals 2.61.

Question 44Moisture content and density determination

What does the unit mass (bulk density) of aggregate in a dry-rodded condition represent?

  1. The mass of solid material only, with all voids removed
  2. The mass of aggregate that fills a unit volume when compacted in a specified manner Correct answer.
  3. The mass of aggregate at its saturated surface-dry state in a loose condition
  4. The ratio of dry mass to saturated mass of a single particle

Explanation

Dry-rodded unit mass expresses the mass of aggregate, including interparticle voids, that fills a container when placed in the specified rodded manner. It is used for converting between mass and volume in proportioning.

Question 45Moisture content and density determination

A container of known volume 0.0100 cubic meters is filled with dry-rodded aggregate whose net mass is 15.6 kg. What is the dry-rodded unit mass, to the nearest kilogram per cubic meter?

  1. 15600 kg per cubic meter
  2. 1560 kg per cubic meter Correct answer.
  3. 156 kg per cubic meter
  4. 15.6 kg per cubic meter

Explanation

Unit mass is the net mass of aggregate divided by the container volume. Dividing 15.6 kg by 0.0100 cubic meters yields 1560 kg per cubic meter.

Question 46Moisture content and density determination

The SSD bulk specific gravity of a fine aggregate is used in mixture proportioning primarily to do which of the following?

  1. Compute the cementitious content required for strength
  2. Determine the abrasion resistance of the aggregate
  3. Convert saturated surface-dry mass of aggregate to its absolute volume Correct answer.
  4. Estimate the air content of the fresh mixture

Explanation

Specific gravity relates mass to absolute volume, so the SSD bulk value lets the proportioner convert the SSD batch mass into the volume the aggregate occupies in the mixture. This supports the absolute volume method of proportioning.

Question 47Moisture content and density determination

Which condition describes aggregate that has been dried in air until its mass is essentially constant but still contains some absorbed water?

  1. Saturated surface-dry
  2. Air-dry Correct answer.
  3. Saturated
  4. Oven-dry

Explanation

Air-dry refers to a field condition in which surface water has evaporated and some but not all pore water may remain. It is not a fixed reference state like oven-dry or saturated surface-dry.

Question 48Moisture content and density determination

A stockpile of sand has free moisture of 5.0 percent. If the batch requires 900 kg of saturated surface-dry sand, what mass of moist sand should be weighed out?

  1. 900 kg
  2. 855 kg
  3. 990 kg
  4. 945 kg Correct answer.

Explanation

The moist mass equals the required SSD mass increased by the free moisture fraction, since free water is carried in addition to the SSD solids and pore water. Multiplying 900 kg by 1.05 gives 945 kg.

Question 49Moisture content and density determination

Why is the saturated surface-dry condition used as a reference state when reporting aggregate specific gravity?

  1. Because it represents a reproducible condition in which permeable pores are filled but no free surface water is present Correct answer.
  2. Because it is the only state in which the aggregate mass is stable over time
  3. Because it corresponds to the maximum density the aggregate can achieve
  4. Because it is the state in which aggregate is easiest to sample in the field

Explanation

The SSD state is reproducible because all permeable pores are filled while the surface is dry, so the measured mass reflects a well-defined pore-water content. This makes specific gravity values comparable between laboratories and materials.

Question 50Moisture content and density determination

A fine aggregate is tested and found to have an absorption of 0.8 percent and a total moisture content of 0.8 percent. What is the condition of the aggregate?

  1. It is drier than the oven-dry condition
  2. It contains free moisture of 0.8 percent
  3. It is essentially at the saturated surface-dry condition Correct answer.
  4. It contains free moisture of 1.6 percent

Explanation

When total moisture equals absorption, all water present is held in the permeable pores and none is free on the surface, which is the saturated surface-dry condition. The free moisture is therefore essentially zero.