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NCMA CCCM practice questions

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Question 1Concrete Masonry

In concrete masonry construction, what is the standard nominal face dimension of a concrete masonry unit (CMU) that produces a 16 in. module when a 3/8 in. mortar joint is used?

  1. 15 3/4 in.
  2. 15 1/2 in.
  3. 15 5/8 in. Correct answer.
  4. 16 in.

Explanation

Nominal dimensions include the mortar joint, so a unit whose specified face is 15 5/8 in. combines with a 3/8 in. joint to give a 16 in. nominal module. This modular coordination is the basis for laying out walls, openings, and bond patterns.

Question 2Concrete Masonry

Which mortar type is specified by ASTM C270 as the highest-compressive-strength mortar commonly used for reinforced masonry and masonry below grade?

  1. Type N
  2. Type O
  3. Type S
  4. Type M Correct answer.

Explanation

ASTM C270 Type M mortar has the highest compressive strength of the common mortar types and is used where high strength or high lateral loads are expected, such as reinforced and below-grade masonry. Type S is the next strongest and Type N is a general-purpose mortar.

Question 3Concrete Masonry

A hollow concrete masonry unit is classified as hollow when its net cross-sectional area in the plane parallel to the bearing surface is less than what percentage of its gross cross-sectional area?

  1. 65 percent
  2. 75 percent Correct answer.
  3. 85 percent
  4. 50 percent

Explanation

ASTM C90 defines hollow load-bearing concrete masonry units as those with a net cross-sectional area less than 75 percent of the gross area in every plane parallel to the bearing surface. Units with net area of 75 percent or more are classified as solid.

Question 4Concrete Masonry

What is the minimum specified compressive strength, f'm, for concrete masonry required by the general structural design provisions of TMS 402 when no higher strength is needed for design?

  1. 1,500 psi Correct answer.
  2. 2,500 psi
  3. 1,000 psi
  4. 2,000 psi

Explanation

TMS 402 establishes a minimum specified compressive strength of 1,500 psi for concrete masonry unless a higher value is required by the design. Designers may specify higher f'm values, but the code floor is 1,500 psi.

Question 5Concrete Masonry

In running bond concrete masonry, what is the standard offset of units in successive courses?

  1. One-third unit
  2. One full unit
  3. One-quarter unit
  4. One-half unit Correct answer.

Explanation

Running bond offsets each course by one-half the unit length, placing vertical joints at the midpoints of the units below. This pattern distributes load and improves wall integrity compared with stacked bond.

Question 6Concrete Masonry

Which term describes the vertical mortar-filled space between the ends of adjacent concrete masonry units in the same course?

  1. Bedding plane
  2. Head joint Correct answer.
  3. Bed joint
  4. Collar joint

Explanation

The head joint is the vertical mortar joint between the ends of adjacent units in a course. The bed joint is the horizontal joint between courses, and the collar joint is the vertical space between wythes in a multiwythe wall.

Question 7Concrete Masonry

Why is grout rather than mortar used to fill the cores of reinforced concrete masonry?

  1. Grout cures faster than mortar
  2. Grout has higher compressive strength and lower shrinkage than mortar Correct answer.
  3. Grout is easier to place in small joints
  4. Grout contains no aggregate

Explanation

Grout is a high-slump mixture proportioned for placement in cores and collar joints; it develops higher compressive strength and lower shrinkage than mortar, which is designed for thin joints. Mortar in cores would not provide the required structural performance.

Question 8Concrete Masonry

What is the purpose of horizontal joint reinforcement in a concrete masonry wall?

  1. To replace vertical reinforcement
  2. To serve as a moisture barrier
  3. To control cracking and improve wall integrity Correct answer.
  4. To provide thermal insulation

Explanation

Horizontal joint reinforcement, typically wire trusses or ladder types placed in bed joints, helps control shrinkage cracking and ties wythes or units together for structural integrity. It is not a substitute for vertical reinforcement.

Question 9Concrete Masonry

A designer specifies Type S mortar for a load-bearing reinforced concrete masonry wall. Which property most directly justifies this choice over Type N?

  1. Improved freeze-thaw durability without air entrainment
  2. Higher compressive strength and better bond for structural loads Correct answer.
  3. Lower cost of materials
  4. Faster setting time

Explanation

Type S mortar provides higher compressive strength and better bond strength than Type N, which is why it is commonly specified for reinforced and load-bearing masonry. Type N is preferred for general, non-structural applications where flexibility and workability are more important.

Question 10Concrete Masonry

A concrete masonry wall is to be built with a specified compressive strength f'm of 2,000 psi. The contractor proposes using units with a net-area compressive strength of 2,500 psi and Type N mortar. What must be verified before accepting the substitution?

  1. That the prism strength based on the proposed materials meets the specified f'm Correct answer.
  2. That the units are lighter than the original specification
  3. That the wall is painted after construction
  4. That the mortar color matches the original

Explanation

The specified f'm is verified through prism testing or by the unit-strength method using the actual units and mortar proposed. A higher unit strength alone does not guarantee the assembly meets f'm, so prism testing or code-recognized evaluation is required.

Question 11Concrete Masonry

During layout, a mason must place a control joint in a long concrete masonry wall. What is the primary function of that control joint?

  1. To accommodate movement and reduce shrinkage cracking Correct answer.
  2. To provide a fire separation
  3. To anchor the wall to the roof diaphragm
  4. To transfer vertical loads to the foundation

Explanation

Control joints are planned vertical separations that allow the wall to move and relieve shrinkage stresses, reducing random cracking. They are not load-transfer, fire-separation, or anchorage elements.

Question 12Concrete Masonry

A wall is designed in stacked bond rather than running bond. Which structural concern should the designer address?

  1. The wall cannot be grouted
  2. Continuous vertical joints reduce resistance to lateral loads Correct answer.
  3. The wall will require no reinforcement
  4. The wall will be too strong

Explanation

Stacked bond aligns head joints vertically over many courses, creating continuous planes of weakness that reduce resistance to lateral loads and crack propagation. Designers often limit stacked bond to non-structural or short walls and add reinforcement.

Question 13Concrete Masonry

What is the principal reason for specifying a water-repellent admixture or integral water repellent in concrete masonry units for an exterior wall?

  1. To reduce the unit's fire rating
  2. To increase the unit's compressive strength
  3. To speed up mortar curing
  4. To reduce water absorption and efflorescence potential Correct answer.

Explanation

Integral water repellents reduce the rate and amount of water absorption by the units, which helps limit moisture penetration and efflorescence. They do not serve as a substitute for proper flashing and drainage detailing.

Question 14Concrete Masonry

A concrete masonry wall requires a bond beam at the top of the wall. What is the typical function of that bond beam?

  1. To serve as a weep hole system
  2. To provide a decorative cap
  3. To distribute concentrated loads and provide continuity Correct answer.
  4. To replace the foundation

Explanation

A bond beam is a course of units with horizontal reinforcement and grout that distributes concentrated loads and ties the wall together. It also provides continuity for anchorage and lateral load resistance.

Question 15Concrete Masonry

Why must mortar joints in concrete masonry be tooled after the mortar has thumbprint-hardened?

  1. To allow the units to be moved
  2. To compact the mortar and improve watertightness Correct answer.
  3. To reduce the mortar's compressive strength
  4. To make the wall easier to paint

Explanation

Tooling compacts the mortar at the joint surface and creates a concave or V profile that sheds water, improving watertightness and durability. Tooling too early or too late can damage the joint or reduce its effectiveness.

Question 16Concrete Masonry

A reinforced concrete masonry shear wall is being detailed. Where should vertical reinforcement typically be placed for maximum effectiveness?

  1. In the collar joint between wythes without grout
  2. On the exterior face without grout
  3. In the mortar bed joints only
  4. In the cells of the units, surrounded by grout Correct answer.

Explanation

Vertical reinforcement in reinforced concrete masonry is placed in the cells of hollow units and fully surrounded by grout so that the steel and masonry act compositely. Grout provides bond and protects the steel.

Question 17Concrete Masonry

A masonry wall is designed with a specified f'm of 1,800 psi. Which test method is commonly used to verify that the masonry assembly achieves the specified compressive strength?

  1. Slump test of mortar
  2. Sieve analysis of sand
  3. Prism test of masonry assemblages Correct answer.
  4. Air content test of grout

Explanation

Prism tests evaluate the compressive strength of a masonry assemblage built from the actual units, mortar, and grout, directly verifying f'm. Mortar slump, sand gradation, and grout air content are quality-control checks but do not measure assembly strength.

Question 18Concrete Masonry

What is the primary purpose of flashing and weep holes at the base of a concrete masonry cavity wall?

  1. To collect and drain water that penetrates the outer wythe Correct answer.
  2. To provide thermal insulation
  3. To anchor the wall to the foundation
  4. To reinforce the wall against wind loads

Explanation

Flashing collects moisture that enters the wall and directs it to weep holes for drainage out of the wall. This detailing protects the inner wythe and interior finishes from water damage.

Question 19Concrete Masonry

A concrete masonry wall is to be constructed in cold weather. Which precaution is most appropriate for the mortar and grout?

  1. Add extra water to improve workability
  2. Eliminate the use of joint reinforcement
  3. Increase the mortar joint thickness
  4. Keep materials above freezing and protect the masonry from freezing until it gains sufficient strength Correct answer.

Explanation

Cold-weather masonry requires that mortar and grout be protected from freezing and that materials be maintained at suitable temperatures until the masonry gains enough strength. Adding water or altering joints would compromise quality.

Question 20Concrete Masonry

An architect specifies a 12 in. nominal concrete masonry wall with a specified compressive strength of 2,500 psi and Type S mortar. Which combination best supports the specified strength?

  1. Units meeting ASTM C90 with the required net-area strength, Type S mortar, and prism verification Correct answer.
  2. Units meeting ASTM C129 with Type O mortar and no testing
  3. Units meeting ASTM C90 with Type N mortar and no testing
  4. Units meeting ASTM C90 with Type S mortar and mortar joint thickness of 1 in.

Explanation

Achieving a specified f'm requires compliant load-bearing units (ASTM C90), the specified mortar type, and verification through prism testing or the unit-strength method. ASTM C129 units are non-load-bearing, and excessive joint thickness weakens the assembly.

Question 21Concrete Masonry

A designer is evaluating two wall systems: a 8 in. hollow concrete masonry wall and an 8 in. grouted concrete masonry wall. Which statement best describes the structural difference?

  1. Grouting the cells reduces the wall's compressive strength
  2. Grouting the cells increases mass, compressive strength, and shear resistance Correct answer.
  3. Grouting the cells has no effect on structural performance
  4. Grouting the cells eliminates the need for reinforcement

Explanation

Filling the cells with grout increases the effective cross-section, mass, and compressive and shear capacity of the wall. Grouting does not eliminate reinforcement requirements and does affect performance.

Question 22Concrete Masonry

A concrete masonry wall is to be constructed with a specified f'm of 3,000 psi using the unit-strength method. Which condition is most critical to verify?

  1. That the unit net-area strength and mortar type together satisfy the code table for f'm Correct answer.
  2. That the wall is built in stacked bond
  3. That the mortar color matches the units
  4. That the units are painted before installation

Explanation

The unit-strength method relies on tables that relate unit net-area compressive strength and mortar type to f'm, so both must meet the specified values. Color, paint, and bond pattern do not determine compressive strength.

Question 23Concrete Masonry

A multiwythe concrete masonry wall has a cavity between wythes. Which detail best prevents water that enters the cavity from reaching the interior?

  1. Eliminating the cavity and using a single wythe
  2. Sealing the cavity completely with mortar
  3. Flashing at the base of the cavity with weep holes through the outer wythe Correct answer.
  4. Installing vapor barrier on the exterior face

Explanation

Flashing at the cavity base collects water and weep holes allow it to drain outward, preventing accumulation and interior penetration. Sealing the cavity with mortar would block drainage and could worsen moisture problems.

Question 24Concrete Masonry

A concrete masonry wall is designed with a specified f'm of 2,000 psi. Prism tests return an average of 2,100 psi with a coefficient of variation of 10 percent. What should the designer consider?

  1. Whether to remove all reinforcement
  2. Whether to reduce the specified f'm
  3. Whether the lower-bound strength accounting for variability still meets f'm Correct answer.
  4. Whether to change the mortar color

Explanation

Acceptance of prism strength accounts for variability, so the designer must check whether the lower-bound value derived from the test results still meets the specified f'm. The average alone may not satisfy the acceptance criteria.

Question 25Concrete Masonry

A concrete masonry wall requires a control joint at a specific location. Which statement best explains why the joint should not be located where a concentrated load is applied?

  1. A control joint interrupts load continuity and can reduce the wall's capacity to resist concentrated loads Correct answer.
  2. Control joints increase the wall's compressive strength at that location
  3. Control joints are decorative and have no structural effect
  4. Control joints eliminate the need for reinforcement

Explanation

Control joints are deliberate planes of weakness that allow movement, so placing one under a concentrated load interrupts load distribution and can reduce capacity. Designers locate joints away from concentrated loads and provide reinforcement where needed.

Question 26Concrete Masonry

What is the standard nominal face dimension of a concrete masonry unit (CMU) that, with a 3/8 in. mortar joint, produces a 16 in. modular length?

  1. 15 1/2 in.
  2. 15 5/8 in. Correct answer.
  3. 15 in.
  4. 16 in.

Explanation

Concrete masonry units are typically specified with nominal dimensions that include the mortar joint. A unit with a nominal length of 16 in. has an actual length of 15 5/8 in., so that when a 3/8 in. mortar joint is added, the module is 16 in. This modular coordination simplifies layout and ensures bond patterns work out with standard details.

Question 27Concrete Masonry

Which mortar type is generally recommended for reinforced concrete masonry walls because it balances high compressive strength with good bond and workability?

  1. Type O
  2. Type S Correct answer.
  3. Type K
  4. Type N

Explanation

Type S mortar is specified for reinforced masonry because it provides high compressive strength (minimum 1800 psi) and good bond strength while remaining workable. Type N is a medium-strength mortar more suited to non-reinforced exterior walls above grade. Type O and Type K are lower-strength mortars used for non-structural applications.

Question 28Concrete Masonry

In concrete masonry construction, what is the primary purpose of a pilaster?

  1. To serve as a decorative vertical band on the wall face
  2. To conceal vertical reinforcement at wall intersections
  3. To provide lateral support and increase the load-carrying capacity of a wall Correct answer.
  4. To allow for expansion and contraction of the wall

Explanation

A pilaster is a vertical projection of masonry built integrally with the wall to add stiffness and load-bearing capacity. It acts like a column to resist lateral loads and can carry concentrated vertical loads. Decorative bands, control joints, and reinforcement concealment are handled by other elements.

Question 29Concrete Masonry

Which of the following is a common method for improving the thermal performance of a single-wythe concrete masonry wall?

  1. Using a darker-colored unit to absorb more solar heat
  2. Applying a vapor retarder on the exterior face
  3. Increasing the mortar joint thickness to 1/2 in.
  4. Filling the cores with loose-fill insulation Correct answer.

Explanation

Filling the hollow cores of concrete masonry units with loose-fill insulation, such as expanded perlite or vermiculite, increases the wall's thermal resistance. Increasing mortar joint thickness reduces thermal performance and is not standard. Darker units increase heat absorption but do not improve insulation value. A vapor retarder on the exterior can trap moisture and is not a thermal improvement.

Question 30Concrete Masonry

What is the minimum specified compressive strength f'm for a concrete masonry wall that is designed as reinforced and load-bearing, according to typical building code requirements?

  1. 2,500 psi
  2. 1,500 psi Correct answer.
  3. 1,000 psi
  4. 2,000 psi

Explanation

The building code generally requires a minimum specified compressive strength f'm of 1,500 psi for reinforced masonry. This value ensures adequate structural performance and is a common baseline for design. Higher strengths are often specified for particular load conditions, but the code minimum is 1,500 psi.

Question 31Concrete Masonry

Which term describes the arrangement of concrete masonry units in which each unit is laid directly over the unit below, with head joints aligned?

  1. English bond
  2. Flemish bond
  3. Stack bond Correct answer.
  4. Running bond

Explanation

Stack bond is a pattern where all head joints are vertically aligned, creating continuous vertical lines. Running bond offsets units by half a unit, while English and Flemish bonds are traditional brick patterns that are not typical for concrete masonry. Stack bond requires special attention to reinforcement because it lacks the interlocking of running bond.

Question 32Concrete Masonry

What is the standard height of a concrete masonry unit course when using a nominal 8 in. high unit and a 3/8 in. mortar joint?

  1. 8 in. Correct answer.
  2. 7 1/2 in.
  3. 8 3/8 in.
  4. 7 5/8 in.

Explanation

A nominal 8 in. high concrete masonry unit has an actual height of 7 5/8 in., and with a 3/8 in. mortar joint the course height becomes 8 in. This modular dimension allows easy calculation of wall heights. The other dimensions listed do not account for the standard joint thickness.

Question 33Concrete Masonry

Which of the following is a primary function of grout in reinforced concrete masonry?

  1. To provide a decorative finish to the wall
  2. To fill the cores and bond the reinforcement to the masonry Correct answer.
  3. To act as a water repellent within the wall
  4. To bond the masonry units together

Explanation

Grout is used to fill the cores of concrete masonry units and to embed reinforcement, creating a composite structural element. It bonds the steel to the masonry and provides additional mass and fire resistance. Mortar is the material that bonds units together, and grout does not serve as a decorative finish or water repellent.

Question 34Concrete Masonry

A concrete masonry wall is to be laid with a specified mortar joint thickness of 3/8 in. Which type of joint is typically used to accommodate minor movement and prevent cracking?

  1. Isolation joint
  2. Construction joint
  3. Expansion joint
  4. Control joint Correct answer.

Explanation

Control joints are intentional planes of weakness that allow controlled cracking due to shrinkage and minor movement. They are typically formed by stopping the mortar joint or using a preformed insert. Construction joints are where work is interrupted, expansion joints accommodate larger movements, and isolation joints separate masonry from other elements.

Question 35Concrete Masonry

When estimating the number of concrete masonry units for a wall, what is the typical allowance for breakage and waste?

  1. 10% to 15%
  2. 1% to 2%
  3. 3% to 5% Correct answer.
  4. 5% to 10%

Explanation

A waste factor of about 3% to 5% is commonly added to the net quantity of concrete masonry units to account for breakage, cutting, and minor site losses. Higher percentages are excessive for typical work, while lower percentages may not cover normal breakage. This allowance helps ensure sufficient material is ordered.

Question 36Concrete Masonry

A concrete masonry wall is designed with a specified compressive strength f'm of 2,000 psi. The contractor proposes to use units with a net area compressive strength of 2,500 psi and Type N mortar. Which statement best evaluates this proposal?

  1. The proposal is unacceptable because the unit strength must be at least 3,000 psi.
  2. The proposal is acceptable because the unit strength exceeds the specified f'm.
  3. The proposal is acceptable if prism tests confirm the required f'm. Correct answer.
  4. The proposal is unacceptable because Type N mortar is not permitted for f'm of 2,000 psi.

Explanation

The specified compressive strength f'm is a property of the masonry assemblage, not just the units. While higher unit strength is beneficial, the mortar type and construction must also be evaluated. Prism tests can verify that the assembled masonry meets f'm; thus the proposal may be acceptable if tests confirm it. Type N mortar is not categorically prohibited for f'm of 2,000 psi, although it may not achieve that strength without testing.

Question 37Concrete Masonry

In a concrete masonry wall, where should horizontal joint reinforcement be placed to be most effective in controlling shrinkage cracks?

  1. In the mortar joint at mid-height of the wall
  2. In the mortar joint near the top of the wall only
  3. In the mortar joint at the bottom of the wall
  4. In every other mortar joint Correct answer.

Explanation

Horizontal joint reinforcement is typically placed in every other mortar joint (often every 16 in. vertically) to provide continuous tensile resistance and control shrinkage cracking. Placing it only at the top, mid-height, or bottom would leave large portions of the wall unreinforced and susceptible to cracking. Even distribution is key to performance.

Question 38Concrete Masonry

A mason is laying concrete masonry units in cold weather (below 40°F). Which precaution is most appropriate to ensure proper mortar curing?

  1. Increase the mortar joint thickness to generate heat
  2. Use hot water to mix the mortar and protect the wall from freezing Correct answer.
  3. Cover the wall with a breathable membrane to retain heat
  4. Add calcium chloride to the mortar mix to accelerate setting

Explanation

In cold weather, mortar ingredients should be heated (using hot water) and the masonry must be protected from freezing until the mortar has gained sufficient strength. Calcium chloride may accelerate set but can cause efflorescence and corrosion and is often limited. Increasing joint thickness does not generate heat, and a breathable membrane does not provide adequate insulation.

Question 39Concrete Masonry

A concrete masonry wall is to be constructed with a specified f'm of 2,500 psi using the unit-strength method. Which condition must be met for this method to be valid?

  1. The units must be tested in accordance with ASTM C140 and the mortar must be Type S or M
  2. The mortar must be tested in accordance with ASTM C780
  3. The wall must be fully grouted
  4. The units must be sampled and tested to establish the relationship between unit strength and prism strength Correct answer.

Explanation

The unit-strength method relies on a pre-established relationship between unit compressive strength and prism strength, typically from code tables or project-specific testing. It requires that the units be sampled and tested to verify their strength, and that the mortar and grout meet certain requirements. Simply using Type S mortar or fully grouting does not validate the method.

Question 40Concrete Masonry

A concrete masonry wall has a control joint at a specific location. Which statement best explains why the joint should be aligned with any opening in the wall?

  1. To reduce the amount of reinforcement required near the opening
  2. To allow for easier placement of grout in the cells
  3. To ensure that movement is accommodated without cracking the masonry around the opening Correct answer.
  4. To simplify the installation of flashing

Explanation

Control joints are placed to accommodate movement and shrinkage, and aligning them with openings helps direct movement away from the corners of openings where stress concentrations occur. This reduces the likelihood of cracking around the opening. Flashing installation, reinforcement quantity, and grout placement are not the primary reasons for this alignment.

Question 41Concrete Masonry

A concrete masonry wall is to be built with a specified f'm of 1,800 psi. The contractor proposes to use the prism test method to verify compliance. Which statement is true regarding the prism test?

  1. Prisms must be tested at 28 days and the average strength must equal or exceed f'm
  2. Prisms must be constructed with the same materials and proportions as the wall and tested in accordance with ASTM C1314 Correct answer.
  3. Prisms can be made with any mortar type as long as the units meet the strength requirement
  4. Prisms are not required if the unit strength exceeds f'm by 10%

Explanation

The prism test method requires that prisms be constructed using the same materials and proportions as the actual wall, and tested according to ASTM C1314. The average prism strength must meet or exceed f'm. Prisms cannot use arbitrary mortar, and unit strength alone does not waive the prism test if that method is chosen.

Question 42Concrete Masonry

A concrete masonry wall is to be constructed with a specified f'm of 3,000 psi. Which combination of materials is most likely to achieve this strength without prism testing?

  1. Type N mortar and units with a net area compressive strength of 3,500 psi
  2. Type S mortar and units with a net area compressive strength of 2,500 psi
  3. Type M mortar and units with a net area compressive strength of 3,000 psi
  4. Type S mortar and units with a net area compressive strength of 4,000 psi Correct answer.

Explanation

To achieve f'm of 3,000 psi without prism testing, the unit-strength method tables typically require higher unit strengths and a stronger mortar. Type S mortar with units of 4,000 psi net area strength is a combination that can satisfy the code tables for 3,000 psi. Type N mortar is generally too weak, and lower unit strengths may not meet the required relationship.

Question 43Concrete Masonry

A concrete masonry wall is designed with a specified f'm of 2,000 psi. Prism tests return an average of 2,100 psi with a standard deviation of 150 psi. What is the coefficient of variation (COV) of the prism test results?

  1. 15.0%
  2. 7.1% Correct answer.
  3. 6.7%
  4. 14.3%

Explanation

The coefficient of variation is the standard deviation divided by the mean, expressed as a percentage: (150 / 2100) × 100 = 7.14%. This indicates the relative variability of the test results. A lower COV suggests more consistent production.

Question 44Concrete Masonry

A concrete masonry wall requires a control joint at a specific location. Which statement best explains why the joint should be continuous through the wall thickness?

  1. To reduce the amount of grout required
  2. To improve the thermal performance of the wall
  3. To allow the wall to move as a unit and prevent random cracking Correct answer.
  4. To simplify the installation of reinforcement

Explanation

A control joint must be continuous through the wall thickness to create a complete plane of weakness, allowing the wall to move and relieve stresses without random cracking. If interrupted, stresses can concentrate and cause cracking elsewhere. Reinforcement, grout quantity, and thermal performance are not the reasons for continuity.

Question 45Concrete Masonry

A concrete masonry wall is to be constructed with a specified f'm of 2,500 psi. The contractor proposes to use the prism test method but wants to reduce the number of prisms tested. Which statement is true regarding the minimum number of prism tests required?

  1. The number of prisms is at the contractor's discretion
  2. At least three prisms must be tested for each 5,000 sq ft of wall area Correct answer.
  3. Two prisms per project are adequate
  4. One prism per 10,000 sq ft is sufficient

Explanation

The building code typically requires a minimum of three prisms to be tested for each 5,000 square feet of wall area, or fraction thereof, when using the prism test method. This provides a statistically meaningful sample. Fewer tests would not meet code requirements.

Question 46Concrete Masonry

A concrete masonry wall is designed with a specified f'm of 2,000 psi. The contractor proposes to use a mortar with a compressive strength of 2,500 psi. Which statement best evaluates this proposal?

  1. The proposal is acceptable because mortar strength exceeds f'm
  2. The proposal is acceptable only if the units have a strength of at least 2,000 psi
  3. The mortar strength alone does not ensure the masonry assemblage meets f'm; prism tests or unit-strength method must be used Correct answer.
  4. The proposal is unacceptable because mortar strength must be less than f'm

Explanation

The compressive strength of the masonry assemblage (f'm) depends on the combination of units, mortar, and grout, not just mortar strength. A high mortar strength does not guarantee that f'm is met. Compliance must be verified by prism tests or the unit-strength method.

Question 47Concrete Masonry

A concrete masonry shear wall is being detailed. Where should vertical reinforcement typically be placed for maximum effectiveness in resisting in-plane shear?

  1. Only at mid-height of the wall
  2. Uniformly distributed throughout the wall length Correct answer.
  3. Only in the outer wythe of a cavity wall
  4. Concentrated at the ends of the wall

Explanation

For in-plane shear resistance, vertical reinforcement is typically distributed uniformly along the wall length to provide consistent shear capacity and crack control. Concentrating it at the ends may be efficient for flexure but not for shear. Mid-height or single-wythe placement would not provide the needed distribution.

Question 48Concrete Masonry

A concrete masonry wall is to be constructed in a region with high seismic risk. Which detailing practice is most important for improving seismic performance?

  1. Reducing the amount of vertical reinforcement to lower stiffness
  2. Using Type N mortar to allow flexibility
  3. Increasing the mortar joint thickness to absorb energy
  4. Providing continuous horizontal reinforcement and adequate anchorage at wall intersections Correct answer.

Explanation

In high seismic regions, continuous horizontal reinforcement and proper anchorage at intersections help tie the structure together and improve ductility. Type N mortar is weaker and not preferred for seismic design. Thicker mortar joints do not absorb seismic energy, and reducing vertical reinforcement would decrease strength and ductility.

Question 49Concrete Masonry

A concrete masonry wall is designed with a specified f'm of 2,500 psi. The contractor proposes to use units with a net area compressive strength of 3,000 psi and Type S mortar. According to the unit-strength method tables, which statement is most accurate?

  1. This combination is unacceptable because the unit strength must be at least 3,500 psi
  2. This combination is always acceptable because both unit and mortar strengths exceed f'm
  3. This combination may satisfy f'm of 2,500 psi if the table for Type S mortar and 3,000 psi units shows an f'm of at least 2,500 psi Correct answer.
  4. This combination is acceptable only if the wall is fully grouted

Explanation

The unit-strength method uses tables that relate unit strength and mortar type to f'm. Whether the combination works depends on the specific table values; if the table shows f'm ≥ 2,500 psi for 3,000 psi units and Type S mortar, it is acceptable. It is not automatically acceptable just because individual strengths exceed f'm, and full grouting is not a condition for the unit-strength method.

Question 50Concrete Masonry

Which mortar type is specified by ASTM C270 as the highest-strength mortar commonly used for reinforced concrete masonry in structural applications?

  1. Type S Correct answer.
  2. Type N
  3. Type M
  4. Type O

Explanation

ASTM C270 defines Type S mortar as a medium-high strength mortar with high tensile bond strength, making it the common choice for reinforced masonry and structural walls. Type M has higher compressive strength but lower bond and workability, so it is reserved for severe compressive loading.