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ACT Mud Walls study materials
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ACT Mud Walls practice questions

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Question 1Soil and Material Selection, Testing and Classification

In an earth mix for mud walls, which soil fraction is chiefly responsible for cohesion and dry strength?

  1. Silt
  2. Clay Correct answer.
  3. Sand
  4. Gravel

Explanation

Clay particles are plate-shaped and carry surface charges that bind the larger sand and silt grains together, giving the mix cohesion and strength once dry. Gravel and sand act mainly as inert filler and provide friction and bulk, while silt contributes very little binding power.

Question 2Soil and Material Selection, Testing and Classification

A moist soil sample feels gritty between the fingers and falls apart when squeezed into a ball. Which fraction does this behaviour most strongly indicate?

  1. Sand Correct answer.
  2. Clay
  3. Silt
  4. Organic matter

Explanation

Grittiness combined with an inability to hold a moulded shape is the classic field sign of a sandy soil, because coarse grains slide past one another rather than sticking. Clay feels soapy and holds shape well, while silt feels smooth and floury with only slight cohesion.

Question 3Soil and Material Selection, Testing and Classification

At what temperature is a soil sample normally oven-dried to determine its moisture content?

  1. 220 degrees Celsius
  2. 85 degrees Celsius
  3. 60 degrees Celsius
  4. 105 to 110 degrees Celsius Correct answer.

Explanation

The standard oven-drying temperature for moisture content is 105 to 110 degrees Celsius, which drives off free water without decomposing organic matter or altering clay minerals. Mass is recorded once the sample reaches constant mass at that temperature.

Question 4Soil and Material Selection, Testing and Classification

A sieve analysis carried out on a soil sample is used to determine which property?

  1. The organic content
  2. The proportion of particles in each size range Correct answer.
  3. The plasticity of the fines
  4. The moisture-density relationship

Explanation

Sieve analysis separates and weighs the coarse fraction of a soil by particle size, producing a grading curve that shows how much material lies in each size range. Material passing the finest sieve is then tested separately, for example by hydrometer, to complete the size distribution.

Question 5Soil and Material Selection, Testing and Classification

What is the main purpose of mixing chopped straw or other plant fibre into a mud brick mix?

  1. To raise the dry density of the brick
  2. To make the mix waterproof
  3. To speed up the setting reaction
  4. To control shrinkage cracking during drying Correct answer.

Explanation

Fibre acts as a distributed reinforcement that carries tensile strain as the wet brick shrinks, spreading movement over many small cracks instead of one large crack. This is why straw length and quantity are chosen mainly to suit shrinkage behaviour rather than strength alone.

Question 6Soil and Material Selection, Testing and Classification

Why is a soil containing a large amount of decaying organic matter considered unsuitable for mud wall construction?

  1. It decomposes over time and weakens the wall Correct answer.
  2. It prevents the soil from absorbing water
  3. It makes the soil too hard to dig
  4. It gives the wall an uneven colour

Explanation

Organic material continues to break down after construction, so the soil loses volume and binding ability, leaving the wall weaker and prone to cracking and damp. Organic-rich soils also hold water, which worsens durability.

Question 7Soil and Material Selection, Testing and Classification

Which water source is appropriate for mixing earth mortar and mud bricks?

  1. Greywater containing soap and grease
  2. Clean water fit for drinking Correct answer.
  3. Seawater from the site
  4. Run-off water carrying farm salts

Explanation

Mixing water should be clean and free of harmful salts, oils, acids and organic matter, so potable water is the safe default. Contaminated water can retard hardening, introduce soluble salts that cause efflorescence, and weaken the finished wall.

Question 8Soil and Material Selection, Testing and Classification

For routine classification tests such as sieve analysis and Atterberg limits, what type of sample is normally required?

  1. An undisturbed tube sample only
  2. A specimen taken from the finished wall
  3. A single lump cut from the surface
  4. A representative disturbed sample Correct answer.

Explanation

Classification tests describe the index properties of the soil as a whole, so the sample must represent the bulk material and be thoroughly mixed and quartered before testing. Disturbance does not change grain size or plasticity, so an undisturbed sample is unnecessary for these tests.

Question 9Soil and Material Selection, Testing and Classification

A soil sample has a liquid limit of 32 percent and a plastic limit of 14 percent. What is its plasticity index?

  1. 46
  2. 18 Correct answer.
  3. 32
  4. 14

Explanation

The plasticity index is the liquid limit minus the plastic limit, so 32 minus 14 gives 18. This value describes the range of moisture content over which the soil remains workable and plastic.

Question 10Soil and Material Selection, Testing and Classification

In the field ribbon test, which result indicates a soil with a high clay content?

  1. The ribbon breaks as soon as it leaves the fingers
  2. The ribbon hangs several centimetres before breaking Correct answer.
  3. The soil feels gritty and crumbles when pressed
  4. The soil cannot be moulded into a ball at all

Explanation

A long, continuous ribbon that hangs from the fingers shows that the soil has enough clay to hold together under its own weight. Short or broken ribbons indicate a soil dominated by silt and sand with little binding clay.

Question 11Soil and Material Selection, Testing and Classification

A Proctor compaction test on an earth mix is performed to establish which two values?

  1. The maximum dry density and the optimum moisture content Correct answer.
  2. The permeability coefficient and the porosity
  3. The organic content and the sulphate content
  4. The liquid limit and the shrinkage limit

Explanation

Compaction tests compact the same soil at several moisture contents and plot dry density against water content, producing a curve whose peak gives the maximum dry density and the corresponding optimum moisture content. Field compaction is then specified against those values.

Question 12Soil and Material Selection, Testing and Classification

If the same soil is compacted with greater compactive effort, how does its compaction curve typically change?

  1. The maximum dry density rises and the optimum moisture content falls Correct answer.
  2. Both the maximum dry density and the optimum moisture content rise
  3. The maximum dry density falls and the optimum moisture content rises
  4. Neither value changes because they are fixed soil properties

Explanation

Heavier compaction drives out more air at a lower water content, so the peak of the curve moves upward and to the left. The soil therefore reaches a higher dry density at a slightly lower optimum moisture content.

Question 13Soil and Material Selection, Testing and Classification

Which clay mineral group is associated with the greatest volume change when a mud wall wets and dries?

  1. Montmorillonite Correct answer.
  2. Kaolinite
  3. Quartz
  4. Illite

Explanation

Montmorillonite belongs to the smectite group and has an expandable layered structure that takes water between its sheets, causing large swelling and shrinkage. Kaolinite has a stable, non-expanding structure and is therefore preferred in earth construction.

Question 14Soil and Material Selection, Testing and Classification

Which additive is most commonly selected to reduce the plasticity of a highly plastic clay soil before compaction?

  1. Hydrated lime Correct answer.
  2. Ordinary Portland cement
  3. Additional mixing water
  4. Chopped straw

Explanation

Lime reacts with the clay fraction and causes immediate flocculation of the particles, which lowers plasticity and improves workability before any long-term cementing reaction develops. This makes lime the usual first choice for very plastic clay soils.

Question 15Soil and Material Selection, Testing and Classification

What does a well-graded sand contain?

  1. Mostly fine silt-sized particles
  2. Grains that are all angular and flaky
  3. A range of grain sizes from fine to coarse Correct answer.
  4. Grains that are all approximately the same size

Explanation

Well-graded sand contains a continuous spread of particle sizes so that smaller grains fill the voids between larger ones, giving denser packing and better interlock. Poorly graded or uniform sand leaves more void space.

Question 16Soil and Material Selection, Testing and Classification

What does the linear shrinkage test on a soil specimen measure?

  1. The length change of a moulded bar as it dries Correct answer.
  2. The loss of mass on oven drying
  3. The water absorbed by a dry sample
  4. The depth of erosion under a water drop

Explanation

A moulded bar of soil at a standard moisture content is dried and its change in length is measured and expressed as a percentage of the original length. The result indicates how much the soil will shrink and therefore how likely it is to crack in service.

Question 17Soil and Material Selection, Testing and Classification

Why are earth blocks dried to constant mass before their compressive strength is measured?

  1. Because strength depends strongly on moisture content, so a dry baseline is needed Correct answer.
  2. Because the press requires a minimum hardness
  3. Because drying increases the block size
  4. Because wet blocks cannot be placed in a press

Explanation

The strength of an earth block falls sharply as its moisture content rises, so results are only comparable when specimens are tested in a defined, normally dry, condition. Drying to constant mass fixes that condition and removes the variable of residual water.

Question 18Soil and Material Selection, Testing and Classification

In a classification system, what does the group symbol CL represent?

  1. Organic clay of high plasticity
  2. Inorganic clay of low plasticity Correct answer.
  3. Inorganic silt of low plasticity
  4. Well-graded gravel

Explanation

The letter C denotes clay and the letter L denotes a liquid limit below 50 percent, so CL is an inorganic clay of low to medium plasticity. A high liquid limit would be shown by the letter H, as in CH.

Question 19Soil and Material Selection, Testing and Classification

A soil sample has a wet mass of 500 g and a mass of 430 g after oven drying. What is its moisture content?

  1. 18.6 percent
  2. 70.0 percent
  3. 14.0 percent
  4. 16.3 percent Correct answer.

Explanation

The mass of water is 500 minus 430, which is 70 g, and moisture content is expressed as a percentage of the dry mass, so 70 divided by 430 gives about 16.3 percent. Dividing by the total wet mass instead is a common but incorrect shortcut.

Question 20Soil and Material Selection, Testing and Classification

Which laboratory procedure estimates the organic content of a soil by burning off the carbon present?

  1. The Proctor test
  2. Atterberg limit testing
  3. Sieve analysis
  4. Loss on ignition Correct answer.

Explanation

Loss on ignition heats a dried sample to a controlled elevated temperature until the organic carbon is oxidised away, and the resulting mass loss is used as an estimate of organic content. The test must be interpreted with care because some clay minerals and carbonates also lose mass on heating.

Question 21Soil and Material Selection, Testing and Classification

Soil A has a plasticity index of 30 and 40 percent clay; soil B is a well-graded sand with a plasticity index of 9 and 12 percent clay. Which soil is the better candidate for cement stabilisation and why?

  1. Soil B, because cement only works in soils with no fines
  2. Soil A, because more clay gives a stronger cement bond
  3. Soil A, because high plasticity means better compaction
  4. Soil B, because cement performs best in low-plasticity granular soils Correct answer.

Explanation

Cement stabilisation relies on hydration products coating and bonding the grains, and this works most efficiently in granular soils with low plasticity where clay does not consume the cement or interfere with hydration. Highly plastic clays need much more cement, and lime is usually considered first for those soils.

Question 22Soil and Material Selection, Testing and Classification

A soil has a liquid limit of 48 percent, a plastic limit of 22 percent, and a natural moisture content of 40 percent. In what consistency state is it?

  1. Plastic Correct answer.
  2. Semi-solid
  3. Above the liquid limit
  4. Liquid

Explanation

The plastic limit is 22 percent and the liquid limit is 48 percent, so the plastic range spans those values and the natural moisture content of 40 percent lies inside it. The soil is therefore in the plastic state, which means it can be moulded without cracking.

Question 23Soil and Material Selection, Testing and Classification

Soil A compacts to a maximum dry density of 1.85 Mg per cubic metre at an optimum moisture content of 12 percent; soil B reaches 1.75 Mg per cubic metre at 17 percent. Which soil most probably contains more clay?

  1. Soil A, because it needs less water
  2. Neither, because compaction is independent of soil type
  3. Soil A, because it reaches a higher dry density
  4. Soil B, because it has a lower dry density and higher optimum moisture content Correct answer.

Explanation

Clay particles have a large surface area that demands more water for lubrication and they pack less densely than granular grains, so a clay-rich soil typically shows a lower maximum dry density at a higher optimum moisture content. Soil B displays exactly that pattern.

Question 24Soil and Material Selection, Testing and Classification

A candidate soil returns a linear shrinkage of about 12 percent. What is the practical implication for wall construction?

  1. The soil is ideal and needs no adjustment
  2. The soil will not bond and needs more clay
  3. The soil is likely to crack badly and should be modified or stabilised Correct answer.
  4. The soil contains too much sand for moulding

Explanation

A linear shrinkage of around 12 percent is high and indicates that the material will contract strongly on drying, producing wide shrinkage cracks and weak bond with renders. Such a soil is usually amended by blending in sand or stabilising with lime or cement before use.

Question 25Soil and Material Selection, Testing and Classification

A builder blends coarse sand into a highly plastic clay soil. What is the expected effect on the mix?

  1. Lower plasticity and reduced drying shrinkage Correct answer.
  2. Higher shrinkage with no change in plasticity
  3. Higher plasticity and increased water demand
  4. No change, because sand is chemically inert and clay controls all behaviour

Explanation

Adding sand reduces the proportion of active clay in the mix and creates a stiffer, better-graded skeleton, so the material becomes less plastic and shrinks less on drying. Sand is chemically inert, but by diluting the clay fraction it still changes the physical behaviour of the mix.

Question 26Soil and Material Selection, Testing and Classification

In a sieve analysis of an earth material, particles that pass the 4.75 mm sieve and are retained on the 0.075 mm sieve are classified as which fraction?

  1. Sand Correct answer.
  2. Clay
  3. Silt
  4. Gravel

Explanation

The conventional size boundaries place gravel above 4.75 mm, sand between 4.75 mm and 0.075 mm, and fines below 0.075 mm. Material in the middle window is therefore the sand fraction, regardless of its mineralogy.

Question 27Soil and Material Selection, Testing and Classification

Which laboratory device determines the liquid limit of a soil by measuring the penetration depth of a metal cone?

  1. Sieve shaker
  2. Proctor hammer
  3. Cone penetrometer Correct answer.
  4. Sand cone

Explanation

The cone penetrometer method relates penetration depth to moisture content to establish the liquid limit. It is an alternative to the Casagrande cup and is widely used because it is less operator-dependent.

Question 28Soil and Material Selection, Testing and Classification

The specific gravity of soil solids typically falls within which range?

  1. 2.60 to 2.80 Correct answer.
  2. 0.60 to 0.80
  3. 4.50 to 5.00
  4. 1.20 to 1.40

Explanation

Most soil grains are silicate minerals such as quartz, whose specific gravity is about 2.65. Values for common soils therefore cluster between roughly 2.60 and 2.80, with higher values suggesting heavy minerals or iron content.

Question 29Soil and Material Selection, Testing and Classification

In a compaction test, the optimum moisture content is the moisture content at which the soil achieves what condition?

  1. The soil crumbles when rolled
  2. The soil becomes fully saturated
  3. The sample reaches its liquid limit
  4. The maximum dry density is achieved Correct answer.

Explanation

The compaction curve plots dry density against moisture content and peaks at the optimum moisture content. At that point, water lubricates the particles enough for dense packing without occupying too much of the void space.

Question 30Soil and Material Selection, Testing and Classification

The plastic limit of a soil is defined as the moisture content at which which behaviour is observed?

  1. The soil flows under its own weight
  2. Volume change stops during drying
  3. A 3 mm soil thread begins to crumble when rolled Correct answer.
  4. The soil passes the 0.075 mm sieve

Explanation

The plastic limit is the lower boundary of the plastic state, found by rolling a thread until it breaks into short pieces at about 3 mm diameter. Below this moisture content the soil behaves as a semi-solid rather than a plastic material.

Question 31Soil and Material Selection, Testing and Classification

A hydrometer analysis is performed to determine the particle-size distribution of which portion of a soil sample?

  1. Fines finer than 0.075 mm Correct answer.
  2. Soluble salts only
  3. Gravel coarser than 4.75 mm
  4. Organic matter only

Explanation

Sedimentation methods such as the hydrometer test use Stokes law to sort particles too small to be separated reliably by sieves. They therefore cover the fines fraction passing the 0.075 mm sieve, including silt and clay sizes.

Question 32Soil and Material Selection, Testing and Classification

A gradation test gives D60 = 0.60 mm and D10 = 0.15 mm. What is the coefficient of uniformity?

  1. 9.0
  2. 0.25
  3. 0.90
  4. 4.0 Correct answer.

Explanation

The coefficient of uniformity is the ratio D60 divided by D10. Substituting the values gives 0.60 divided by 0.15, which equals 4.0, indicating a moderately uniform material.

Question 33Soil and Material Selection, Testing and Classification

A compacted earth sample has a bulk density of 2.05 Mg per cubic metre and a moisture content of 18 percent. What is its dry density?

  1. 1.74 Mg per cubic metre Correct answer.
  2. 0.37 Mg per cubic metre
  3. 1.68 Mg per cubic metre
  4. 2.23 Mg per cubic metre

Explanation

Dry density equals bulk density divided by one plus the moisture content expressed as a decimal. Dividing 2.05 by 1.18 gives approximately 1.74 Mg per cubic metre, the density of the soil solids plus voids alone.

Question 34Soil and Material Selection, Testing and Classification

A sand replacement test carried out on a finished earth wall or layer is used to determine which property?

  1. The liquid limit of the fill
  2. The plasticity index of the mix
  3. The organic content of the borrow soil
  4. The in-place dry density of the compacted material Correct answer.

Explanation

The sand replacement method measures the volume of a excavated hole and the mass of soil removed, giving field density. Combined with a moisture content determination, it yields the in-place dry density for comparison with the specified compaction.

Question 35Soil and Material Selection, Testing and Classification

A clay soil contains 30 percent clay-sized particles and has a plasticity index of 18. What is its activity ratio?

  1. 5.40
  2. 0.60 Correct answer.
  3. 0.17
  4. 1.67

Explanation

Activity is the plasticity index divided by the percentage of clay-sized particles. Here 18 divided by 30 gives 0.60, which indicates a soil of normal to low activity for its clay content.

Question 36Soil and Material Selection, Testing and Classification

Which test on an earth sample is most directly relevant to predicting efflorescence on a finished mud wall?

  1. Proctor compaction test
  2. Liquid limit test
  3. Sieve analysis
  4. Total soluble salts test Correct answer.

Explanation

Efflorescence occurs when soluble salts migrate to the wall surface with moisture and crystallise as the water evaporates. A total soluble salts determination therefore gives the most direct indication of that risk.

Question 37Soil and Material Selection, Testing and Classification

The shrinkage limit of a soil is the moisture content below which which condition applies?

  1. The plasticity index becomes zero
  2. The soil behaves as a liquid
  3. No further volume reduction occurs on drying Correct answer.
  4. The soil can no longer be rolled into a thread

Explanation

The shrinkage limit marks the transition from a semi-solid to a solid state, where the soil stops shrinking as it dries further. Below this moisture content, air enters the voids instead of the volume continuing to reduce.

Question 38Soil and Material Selection, Testing and Classification

The zero air voids line on a compaction curve indicates which condition?

  1. The specific gravity of the soil solids
  2. The plastic limit of the compacted soil
  3. The peak of the compaction curve
  4. Full saturation at a given water content Correct answer.

Explanation

The zero air voids line gives the dry density at which all voids are filled with water for each moisture content. No compaction result can plot to the right of this line, because soil cannot be denser than the fully saturated condition.

Question 39Soil and Material Selection, Testing and Classification

A field dry density of 1.72 Mg per cubic metre is obtained, and the laboratory maximum dry density for the same mix is 1.85 Mg per cubic metre. What is the relative compaction?

  1. 7 percent
  2. 93 percent Correct answer.
  3. 107 percent
  4. 108 percent

Explanation

Relative compaction is the field dry density divided by the laboratory maximum dry density, expressed as a percentage. Dividing 1.72 by 1.85 gives 0.930, so the layer has reached about 93 percent of the reference density.

Question 40Soil and Material Selection, Testing and Classification

A particle-size distribution curve that is steep and covers only a narrow range of particle sizes indicates which soil condition?

  1. A soil with high clay activity
  2. A uniformly graded soil with poor interlocking Correct answer.
  3. A soil with high organic content
  4. A well-graded soil with good packing

Explanation

A steep curve means most particles fall within a small size interval, which is the signature of a uniformly graded material. Such soils lack the range of sizes needed to fill voids, so their interlocking and density are generally poorer.

Question 41Mix Design, Moisture Control and Additives

In earth construction, what does 'optimum moisture content' refer to?

  1. The maximum quantity of water the soil can hold before it becomes fully saturated
  2. The water content at which a soil compacts to maximum dry density Correct answer.
  3. The moisture content at which clay particles begin to swell and lose strength
  4. The amount of water needed to make a mud mix workable by hand

Explanation

Optimum moisture content is read from the peak of the compaction curve produced by a Proctor test. Below it, friction between particles prevents tight packing; above it, water occupies space that soil could fill. Both conditions reduce dry density and strength.

Question 42Mix Design, Moisture Control and Additives

What is the primary reason for adding chopped straw to a mud wall mix?

  1. To make the mix waterproof against rising damp
  2. To increase the dry density of the compacted earth
  3. To accelerate the chemical reaction between clay minerals and mixing water
  4. To reduce shrinkage cracking and improve tensile strength Correct answer.

Explanation

Chopped straw acts as discrete reinforcement: it bridges the shrinkage cracks that open as wet earth dries and carries tensile stress that plain earth cannot. Fibres do not densify the mix or block the movement of water.

Question 43Mix Design, Moisture Control and Additives

Which particle-size fraction in a soil acts as the natural binder in unstabilised mud?

  1. Silt
  2. Sand
  3. Clay Correct answer.
  4. Gravel

Explanation

Clay particles are plate-like and develop cohesive and electrostatic bonds with water and neighbouring particles, giving unstabilised earth its strength. Sand, silt and gravel act largely as inert filler.

Question 44Mix Design, Moisture Control and Additives

Why is a damp-proof course placed near the base of a mud wall?

  1. To provide a mechanical key for the render applied to the wall face
  2. To increase the compressive strength of the lower courses of the wall
  3. To allow moisture trapped inside the wall to escape freely to the outside
  4. To break the capillary path that draws ground water upward Correct answer.

Explanation

Earth is a porous material, so groundwater rises through it by capillary suction and softens and erodes the base of the wall. A damp-proof course is a continuous low-permeability layer that interrupts that path just above ground level.

Question 45Mix Design, Moisture Control and Additives

What is the main consequence of using a soil with too high a clay content in a mud mix?

  1. The mix shrinks and swells markedly, causing cracks Correct answer.
  2. The mix loses all cohesion and crumbles into loose particles when handled
  3. The mix becomes far too permeable to rainwater
  4. The mix cannot be compacted at all

Explanation

Clay swells as it absorbs water and shrinks as it dries, so a clay-rich mix moves dimensionally and cracks. Sand and silt fractions are needed to dilute the clay and restrain that movement.

Question 46Mix Design, Moisture Control and Additives

Lime stabilization is generally most effective in which type of soil?

  1. Organic peat with a high humus content
  2. Plastic clayey soils with a significant clay fraction Correct answer.
  3. Uniform fine sand containing less than five percent fines
  4. Clean, well-graded gravel containing essentially no fines

Explanation

Lime gains its strength in earth through the pozzolanic reaction between calcium and the silica and alumina of clay minerals. Granular or organic soils lack the reactive clay or interfere with the reaction, so lime is wasted there.

Question 47Mix Design, Moisture Control and Additives

Rice husk ash is used in mud mixes mainly because:

  1. It raises the water demand of the mix and slows compaction
  2. Its amorphous silica reacts with lime to form cementitious compounds Correct answer.
  3. It coats the clay particles and prevents them from drying out too quickly
  4. It acts as a coarse aggregate that bulks out the mix and reduces cost

Explanation

Rice husk ash is a pozzolan: its amorphous silica reacts with calcium hydroxide from lime or cement to form calcium silicate hydrate. That increases strength and reduces permeability, and the ash is far too fine to act as aggregate.

Question 48Mix Design, Moisture Control and Additives

Why should cement-stabilised mud blocks be moist-cured for about a week after casting?

  1. To make the blocks easier to remove from their moulds
  2. To increase the clay content of the block through prolonged hydration
  3. To supply water for continued cement hydration and strength gain Correct answer.
  4. To dissolve the unreacted cement particles so they can recrystallise

Explanation

Cement hardens by hydration, a chemical reaction that consumes water over days and weeks. If the block dries out early, hydration stops, strength is lost and shrinkage cracks open, so moist curing keeps the reaction going.

Question 49Mix Design, Moisture Control and Additives

A soil has a liquid limit of 45% and a plastic limit of 20%. What is its plasticity index and what does it indicate?

  1. 65%; a highly plastic soil that will shrink and swell severely
  2. 2.25%; a soil with negligible clay content and no cohesive strength
  3. 25%; a non-plastic soil that needs no stabiliser and will not shrink
  4. 25%; a moderately plastic soil that will shrink noticeably on drying Correct answer.

Explanation

The plasticity index is the liquid limit minus the plastic limit, so 45 minus 20 gives 25%. A plasticity index around 25% indicates moderate plasticity: the soil is workable but will shrink on drying and may need sand or a stabiliser.

Question 50Mix Design, Moisture Control and Additives

Why does a high organic matter content reduce the effectiveness of cement stabilization in earth?

  1. Organic acids interfere with cement hydration Correct answer.
  2. Organic matter absorbs all of the mixing water before the cement can use it
  3. Organic matter raises the clay fraction, which dilutes the cement powder
  4. Organic matter makes the soil too alkaline for cement to set

Explanation

Humic and fulvic acids in organic matter retard cement hydration and consume the calcium hydroxide needed for strength. Organic soils are therefore avoided, pretreated with lime, or given much higher cement contents.