Tentative Guidelines for the Use of Lime-Fly Ash Concrete as Pavement Base or Sub-Base

The Introduction of IRC 60 covers key specifications and guidelines for lime-fly ash concrete used in road construction. Important points include:

• Lime-fly ash concrete should achieve a minimum 28-day compressive strength of 40-60 kg/cm² in the field, with laboratory mixes designed for 1.25 times this strength to allow for field variances (Clause 4.2.2).
• Both cube and beam test samples are recommended to determine compressive and flexural strength; if beam samples are not feasible, flexural strength can be assumed as 1/6th of compressive strength (Clause 4.2.3).
• Batching should be by weight, mixing in power-driven mixers; compaction by 6-10 tonne smooth or vibratory rollers depending on aggregate hardness (Clauses 5.1, 5.2).
• Subgrade preparation requires checking line, grade, and firmness, with moistening to prevent water absorption before laying concrete (Clause 6).
• Thickness for base course in flexible pavement should be at least 10 cm, designed per CBR method with equivalency factor 1.25-1.5 (Clause 1.5).

Typical mix proportions and strengths are given in Table 1, reproduced below:

These guidelines ensure quality and durability of lime-fly ash concrete layers in pavement construction.

Sources: Clause 1.5, Clause 4.2.2, Clause 4.2.3, Clause 5.1, Clause 5.2, Clause 6, Table 1

The IRC 60 provides tentative guidelines for the thickness design of Lime-Fly Ash Concrete (LFAC) used as pavement base or subbase layers. Although specific formulas or tables are not explicitly stated in the retrieved context, the design generally involves considering the structural capacity of LFAC to distribute loads and its stiffness characteristics. Typically, thickness design accounts for traffic loading, subgrade strength, and material properties of LFAC. The design aims to ensure adequate thickness to prevent excessive deformation and cracking under repeated loads. For detailed design, refer to the full IRC 60 document sections on LFAC base/subbase, which include empirical formulas and design charts based on traffic and subgrade conditions. Key specifications include proper mix design of lime and fly ash, curing, and compaction to achieve desired strength and durability.

Sources: Clause 2 (Tentative Guidelines for LFAC Base/Subbase)

Key materials and specifications for Lime-Fly Ash Concrete per IRC 60 are:

• Lime: Use hydrated lime of Class C variety as per IS: 712-1972, with minimum 60% purity (Clause 3).
• Fly Ash: Should conform to IS: 3812 (Part II)-1966 (Clause 3).
• Aggregates: Coarse aggregate to conform to IS: 383-1970 or IS: 3068-1965 (broken brick) or IS: 2686-1964 (cinder). Fine aggregate as per IS: 383-1970 or IS: 3182-1967 (Clause 3.3).
• Water: Clean, potable water free from deleterious substances (Clause 3.3).

Mix Design Criteria:

• Target 28-day compressive strength: 40-60 kg/cm² (Clause 4.1).
• Workability: Zero slump for field compaction by rolling (Clause 4.1).

Typical Mix Proportions and Strengths (by weight):

• Minimum thickness for base course in flexible pavement: not less than 10 cm (Clause 1.5).
• For subbase under rigid pavement, 10 cm lime-pozzolana concrete is recommended (Clause 2.2).

This summary provides essential material specs, mix proportions, and design criteria for lime-fly ash concrete as per IRC 60.

Sources: Clause 1.5, Clause 2.2, Clause 3, Clause 3.3, Clause 4.1, Clause 4.2.1, Table 1

For proportioning Lime-Fly Ash Concrete as per IRC 60, the key points are:

• Mix Design Criteria: The concrete should achieve a minimum compressive strength of 40-60 kg/cm² at 28 days with zero slump for low workability, as per Clause 4.1.

• Materials: Lime should be Class C hydrated lime with at least 60% purity (Clause 3). Fly ash must conform to IS: 3812 (Part II)-1966. Aggregates should conform to IS: 383-1970 or related standards (Clause 3.3).

• Typical Mix Proportions and Strengths (Clause 4.2.1, Table 1):

• Thickness: For base course in flexible pavement, minimum thickness is 10 cm (Clause 1.5). For subbase under rigid pavement, 10 cm thickness is recommended (Clause 2.2).

This mix design is by trial and error, considering fly ash lime-reactivity of 40-50 kg/cm² and lime purity of 60%.

Sources: Clause 1.5, Clause 2.2, Clause 3, Clause 3.3, Clause 4.1, Clause 4.2.1, Table 1

For batching, mixing, and compaction of lime-fly ash concrete as per IRC 60:

• Batching: Materials should be batched by weight using approved weigh-batching equipment; volume batching is allowed only if unavoidable. Water is measured by volume with calibrated containers. Proportions must consider moisture in aggregates, lime, and fly ash (Clause 7.4, 5.1).

• Mixing: Use power-driven mixers of approved type, ensuring uniform homogeneous mixing without overloading. Mixing time should be 1-2 minutes (Clause 7.4).

• Compaction: Use 8-10 tonne smooth wheel rollers for hard aggregates or 6-8 tonne for softer aggregates; vibratory rollers of equivalent capacity are also permitted. Rolling starts from edges towards the center, with adequate passes to ensure full compaction. Compaction must be completed within 4 hours of mixing (Clause 7.6, 5.2).

• Typical Mix Proportions and Strengths (Table 1):

These guidelines ensure proper batching, mixing, and compaction for durable lime-fly ash concrete pavement layers (Clauses 7.4, 7.6, 5.1, 5.2).

Sources: Clause 7.4, Clause 7.6, Clause 5.1, Clause 5.2, Table 1

The retrieved context from IRC 60 does not provide explicit formulas, tables, or detailed specifications for the preparation of subgrade or subbase. However, general practice for subgrade/subbase preparation in flexible pavements includes: compacting the soil to achieve required density, ensuring proper moisture content, and providing a uniform, stable surface free from loose material. Lime-fly ash concrete is tentatively recommended as a pavement base or sub-base material, indicating its use for improved strength and durability. For detailed design and specifications, refer to the full IRC 60 document or related guidelines on lime-fly ash concrete application.

Key construction specifications for lime-fly ash concrete per IRC 60 include:

• Mix Design: Design for 1.25 times the required 28-day field compressive strength (40-60 kg/cm²) to allow for field variances (Clause 4.2.2).
• Batching & Mixing: Materials batched by weight; volume batching only if unavoidable. Mixing in power-driven mixers for 1-2 minutes ensuring uniformity (Clause 5.1, 7.4).
• Compaction: Use 8-10 tonne smooth wheel roller for hard aggregates or 6-8 tonne for soft aggregates; vibratory rollers acceptable. Rolling starts from edges inward, completed within 4 hours of mixing (Clause 5.2, 7.6).
• Subgrade Preparation: Check line, grade, cross-section; rectify irregularities; saturate subgrade 6-20 hours before laying (Clause 6).
• Joints: Only construction joints at day-end with 30° chamfered edges (Clause 7.7).
• Curing: Cover with wet gunny bags for 48 hours, then wet sand or frequent watering for minimum 7 days (preferably 14) without ponding (Clause 7.7).
• Surface Course: For flexible pavements, provide intermediate bitumen-bound layer plus wearing course ≥10 cm to prevent reflection cracks; rigid pavements can have direct cement concrete wearing course (Clause 8).

Typical Mix Proportions and Strengths (Table 1):

Quality Control Tests (Table 2):

These specifications ensure proper strength, durability, and performance of lime-fly ash concrete in pavement construction.

Sources: Clause 4.2.2, Clause 5.1, Clause 5.2, Clause 6, Clause 7.4, Clause 7.6, Clause 7.7, Clause 8, Table 1, Table 2

As per IRC 60 Clause 7.1, lime should be stored under cover in a dry place to prevent moisture ingress. Quick lime slaked on site must be left overnight for complete slaking and cooling, and used within about one week to avoid carbonation by aeration. If supplied as dry hydrated lime in airtight bags, storage can extend up to 3 months. Handling requires care to maintain dryness and prevent premature carbonation.

Key points:

• Store lime under cover, dry place.
• Slaked lime used within 1 week if slaked on site.
• Dry hydrated lime in airtight bags can be stored up to 3 months.

This ensures lime quality for lime-fly ash concrete production and durability.

No specific formulas or tables for lime storage are provided in Clause 7.1, but these handling guidelines are critical for maintaining lime reactivity and preventing quality loss.

Sources: Clause 7.1

As per IRC 60 Clause 7.2, fly ash should be stored and handled carefully due to its fine, air-borne nature. Key specifications include:

• Fly ash may be bagged or soaked with water at the top during transport and storage to prevent dust.
• When not bagged, store in trapezoidal pits with the top surface kept wet or covered with tarpaulins.

Additionally, fly ash used in lime-fly ash concrete should conform to IS: 3812 (Part II)-1966 (Clause 3).

For mix design, typical lime-fly ash concrete proportions and strengths are given in Table 1 (Clause 4.2.1):

These mixes target 40-60 kg/cm² compressive strength at 28 days with low workability (zero slump) for semi-rigid pavement layers (Clause 4.1).

Summary:

• Store fly ash wet or bagged to prevent dust (Clause 7.2).
• Use IS: 3812 compliant fly ash (Clause 3).
• Follow mix proportions and strengths as per Table 1 for lime-fly ash concrete (Clause 4.2.1).

Sources: Clause 7.2, Clause 3, Clause 4.1, Clause 4.2.1

For Storage and Handling of Aggregates as per IRC 60, Clause 7.3 and related clauses:

• The maximum size of coarse aggregate should generally not exceed 40 mm for 10 cm thick lime-fly ash concrete layers. For thicker layers, multilayer construction is recommended (Clause 2.5).
• Aggregate/binder (lime + fly ash) ratio by weight is approximately 2.5 to 3.5 for 28-day compressive strength of 40-60 kg/cm², with water content about 10-11% by weight of total dry materials when using crushed stone (Clause 2.5).
• Aggregates should be stored to avoid contamination and moisture changes; moist fly ash aids mixing (Clause 7.4).
• Batching should be by weight using approved equipment; water measured by volume (Clause 7.4).
• Compaction by rolling should start from edges progressing inward, with adequate passes to ensure full compaction within 4 hours of mixing (Clause 7.6).

No explicit tables or formulas for storage are given, but adherence to these specifications ensures proper handling and quality of aggregates in lime-fly ash concrete.

Sources: Clause 7.3, Clause 2.5, Clause 7.4, Clause 7.6

For batching and mixing of lime-fly ash concrete as per IRC 60 Clause 7.4 and related clauses:

• Batching: Materials should be batched by weight using approved weigh-batching equipment; volume batching is permitted only if unavoidable. Water is measured by volume with calibrated containers. Proportions must consider free moisture in aggregates and moisture in lime and fly ash.

• Mixing: Use power-driven mixers of approved type, ensuring uniform and homogeneous mixing. Avoid overloading the mixer and provide adequate mixing time of 1-2 minutes for uniformity.

• Typical Mix Proportions and Strengths (Table 1):

• Water Content: Typically about 10-11% by weight of dry materials.

• Aggregate Size: Max coarse aggregate size generally limited to 40 mm for 10 cm thick layers.

• Additional Notes: Moist fly ash aids mixing; compaction should be done within 4 hours of mixing; rolling compaction is recommended.

These specifications ensure proper batching, mixing, and quality control for lime-fly ash concrete as a semi-rigid pavement layer.

Sources: Clause 7.4, Clause 4.2.1, Table 1, Clause 2.5

As per IRC 60 Clause 7.5, transportation and placement of lime-fly ash concrete must ensure the compacted layer attains the required depth, slope, and camber. A surcharge of about 20-25% of the layer thickness is recommended to aid compaction, with the exact amount determined by field trials. Segregation during transport and placement must be avoided; any segregated portions should be thoroughly mixed back into the batch during spreading. Compaction (Clause 7.6) should start from edges progressing inward, with adequate rolling passes to achieve full compaction. Surface grade and camber must be checked and corrected during compaction. Compaction must be completed within 4 hours of mixing, and if laid in two layers, the second layer should be placed within 2-3 hours after compacting the first, per IS:5817-1970. Mixing time is 1-2 minutes in power mixers (Clause 7.4).

Sources: Clause 7.4, Clause 7.5, Clause 7.6, IS:5817-1970

Key specifications and procedures for compaction of lime-fly ash concrete per IRC 60 are as follows:

• Compaction should be done by rolling using an 8 to 10 tonne smooth wheel roller for harder aggregates or 6 to 8 tonne roller for softer aggregates; vibratory rollers of equivalent capacity may also be used (Clause 5.2).
• Rolling must start from the outer edges progressing towards the middle, or from the lower edge to higher edge on superelevated sections (Clause 7.6).
• Adequate number of passes should be given to ensure full compaction (Clause 7.6).
• Surface grade and camber must be checked during compaction; irregularities corrected by adding or removing material (Clause 7.6).
• Compaction must be completed within 4 hours of mixing as per IS:5817-1970 (Clause 7.6).
• For two-layer construction, the second layer should be laid within 2-3 hours after compaction of the first layer (Clause 7.6).

These ensure proper density and strength development of the lime-fly ash concrete base/subbase layer.

Sources: Clause 5.2, Clause 7.6, IS:5817-1970

As per IRC 60 Clause 7.7, joints in lime-fly ash concrete pavements are restricted to construction joints only, located at the end of the day's work or at each successive length for rolling. These joints should be formed by chamfering the edge of the laid concrete at about 30° and then placing fresh concrete against it. After laying and compaction, curing must be done for at least 7 days (preferably 14) by covering with wet gunny bags or hessian, followed by wet sand or frequent watering without ponding. No traffic is allowed before the top courses are placed. This ensures proper bonding and durability at joints.

Key specifications for joints:

• Only construction joints allowed (no other joints)
• Chamfer edge at ~30°
• Curing for minimum 7 days
• No traffic before overlay

This is critical to prevent cracking and ensure structural integrity of the lime-fly ash concrete base or sub-base.

Additional relevant details on mix design, curing, and quality control are provided in IRC 60 but specific joint formulas or tables beyond Clause 7.7 are not given.

Sources: Clause 7.7

As per Clause 7.9 of IRC 60, rectification of surface irregularities in lime-fly ash concrete should be done while the mix is still plastic by checking line, level, grade, and surface finish following Chapter 7 of IRC SP-11-1973. Any irregularities left after hardening must be corrected by cutting out sufficiently large patches and relaying to specification. No specific formulas or tables are provided for rectification, but the process emphasizes early detection and correction during plastic state and patch repair after hardening. Additionally, curing for at least 7 days (preferably 14) is required to ensure proper strength and surface quality (Clause 7.7).

Sources: Clause 7.7, Clause 7.9

As per IRC 60, the Surface Course specifications for flexible pavements with lime-fly ash concrete base include providing an intermediate bitumen bound layer over the lime-fly ash concrete base to prevent reflection cracking due to thermal/drying shrinkage (Clause 8). This intermediate layer plus the wearing course should have a minimum combined thickness of 10 cm. For rigid pavements with lime-fly ash concrete subbase, the cement concrete wearing course can be laid directly without an intermediate layer due to the rigidity preventing crack reflection (Clause 8).

Regarding joints, no joints except construction joints at the end of the day's work are allowed, formed by chamfering the edge at about 30° (Clause 7.7).

Curing of lime-fly ash concrete base/sub-base should be for at least 7 days, preferably 14 days, with wet gunny bags or hessian followed by wet sand or frequent watering (Clause 7.7).

Quality control tests relevant to surface course materials and base include tests on lime, fly ash, aggregate properties, and strength of cubes as per Table 2 below (Clause 9):

Sources: Clause 7.7, Clause 8, Clause 9, Table 2

Quality control for lime-fly ash concrete as per IRC 60 involves specific tests and frequencies to ensure material and construction standards. Key tests include:

Additionally, mix design should target a minimum 28-day compressive strength of 40-60 kg/cm², with laboratory mixes designed for 1.25 times this strength to allow field variances (Clause 1.25). Batching by weight and mixing in power-driven mixers is recommended, with compaction by 6-10 tonne rollers or equivalent vibratory rollers. Curing should be for at least 7 days, preferably 14, using wet coverings and frequent watering without ponding (Clause 7.7).

These controls ensure durability and performance of lime-fly ash concrete pavement layers.

Sources: Clause 7.7, Table 2, Clause 1.25, Clause 5.1, Clause 5.2