PCCPOUTLINE PDF

SUBGRADE PREPARATION Subgrade is the main part of the any earth work.They are widely used in road, railway and airport runway construction but here we will discuss sequence wise working methodology for the earthwork in subgrade for any highway work. SUBBASE PREPARATION After performing clearing,...

SUBGRADE PREPARATION Subgrade is the main part of the any earth work.They are widely used in road, railway and airport runway construction but here we will discuss sequence wise working methodology for the earthwork in subgrade for any highway work. SUBBASE PREPARATION After performing clearing, grubbing, excavation, embankment, and subgrade preparation, the next step is subbase preparation. The subbase is the layer where the concrete will be placed, and it will be laid on top of the subgrade. Subbase preparation is only undertaken once the subgrade has been confirmed to be firmly and correctly compacted. A California Bearing Ratio (CBR) test is conducted to determine the appropriate thickness of the subbase to be laid on the subgrade. Once the materials for the subbase pass quality testing, they are laid on the surface until the correct thickness and hardness are achieved. The number of subbase layers depends on the design thickness. If the subbase thickness is 150 mm, only one layer is required. However, if the thickness exceeds 150 mm, two or more layers are necessary. For each 200 mm layer of subbase, it must successfully pass the field density test before the next layer is applied. This process continues until the required elevation specified in the plan is reached. During the spreading and compacting of the subbase, the moisture content of the materials is carefully controlled. This is why, in road construction, you may see the materials being moistened or dried. A vibratory roller or compactor is used to ensure the subbase is even, well-compacted, and free of soft spots. To confirm that the subbase is properly compacted, a field density test is conducted again. However, placing the subbase is not a simple task; any errors require redoing the work, as specific standards must be adhered to, especially during project implementation. Improper preparation of the subbase can lead to road failures, such as longitudinal cracks, indicating base failures. Therefore, the construction of the subbase course must be done correctly, as it provides the necessary strength for the road. PCCP Construction The construction methodology for road types varies depending on the classification and specific requirements of the project. For tertiary roads, which connect two towns, and secondary roads, which connect two provinces, specific materials and techniques are used to ensure durability and stability. Primary roads, typically connecting at least two cities, require even more robust construction, including a road thickness of 280mm. The road shoulders are constructed with a thickness of 8 inches and a width of 1.5 meters. When dealing with curves, the shoulder is referred to as "widening on curve," and it must match the thickness of the PCCP. The curb and gutter have a width of 1.65 meters, while the main road is designed with a width of 3.35 meters on both the left and right sides, spanning a length of 4.5 meters. Dowel bars, used in the pavement, are typically calculated by dividing the thickness of the PCCP by 8 and rounding up, usually resulting in a 32mm diameter. Weakened plane joints are aligned with any cracks that develop in the concrete to guide further cracking. The dowel bars are plain, while the tie bars are corrugated, with the corrugated bars measuring 0.60 meters in length. Tie bars are deformed rebars or connectors used to hold the faces of rigid slabs together to maintain the connection between them. However, tie bars do not transfer loads. They are commonly used in longitudinal joints in concrete pavement. Dowel bars are placed at the transverse joints of concrete pavement and they take part in load transfer from one slab to its adjacent slab. The dowel bars also allow axial thermal expansion and contraction of the concrete slab along the axis of the dowel. 1. Proportioning and Mixing Concrete A slump test should be performed on the freshly mixed cement. The concrete must arrive at the project site within a 45-90 minute window from the time water is added to the mixture. Upon arrival, conduct another slump test, and if it passes, the concrete can be poured. Proportioning: o Base Proportions: Determined based on the predetermined cement content or designed for the minimum flexural strength required by the contract. o Slump Testing: Conducted according to AASHTO T 119 (ASTM C 143). o Air Content Testing: Conducted according to AASHTO T 152 (ASTM C 231). o Specimen Testing: Make, cure, and test specimens according to AASHTO T 23, T 22, and T 97.  o Moisture Adjustments: Adjust batch weights periodically to account for actual moisture content in the aggregates. Mixing Concrete: o Continuous Mixing: Ensure continuous mixing with no more than 30 minutes between consecutive batches. Concrete consistency should resemble that of "tae ng kalabaw," ensuring the mix is neither too wet nor too dry. Type 1 cement or Type 1P is preferred for this type of construction, while Type 1T, which sets more slowly, is used for plastering masonry or honeycombs. 2. Concrete Placement Concrete should be placed and remain undisturbed for no more than 30 minutes. If the mixer does not return within 30 minutes, any excess concrete beyond 1.5 meters must be removed. Typically, 9.5 to 10 bags of cement are used per cubic meter of concrete. 3. Finishing Initial Finishing: Strike-Off and Consolidation: After placing concrete, strike it off to conform to the required cross-section, ensuring proper consolidation and surface finish. Machine Finishing: Use a finishing machine to strike off, screed, and consolidate the concrete. Maintain uniform ridges of concrete ahead of the front screed during the first pass. Vibratory Finishing: Surface and internal vibrators must meet frequency requirements. Vibrate the concrete uniformly to achieve satisfactory density, ensuring vibrators do not come into contact with reinforcement or forms. 4. Curing Next, proceed with curing. Once the concrete has achieved the proper hardness, a broom finish should be applied to the surface. The broom finish creates a rough texture on the road, providing friction to prevent vehicle tires from slipping. Afterward, apply a curing compound. There are various methods for curing concrete. Burlap mats or abaca sacks can be placed on top of the concrete and kept wet for seven days. Straw curing is another option, where straw is placed on top of the burlap mats after they are laid. Curing Methods: o Cotton/Burlap Mats: Saturate mats with water and place them over the pavement, ensuring intimate contact with the surface. Keep mats fully wetted for at least 72 hours. o Waterproof Paper: Cover the pavement with waterproof paper, ensuring it remains in contact with the surface and edges. o Impervious Membrane: Apply a white pigmented curing compound immediately after finishing. The compound should be uniformly sprayed to cover the entire surface. o Polyethylene Sheeting: Cover the pavement with sheeting, ensuring it extends beyond the slab edges and remains in contact with the surface. Curing Maintenance: Maintain curing coverage continuously for 72 hours, and do not allow the concrete to be exposed for more than 30 minutes between curing stages. 5. Cutting Contraction joints should be placed every 4.5 meters with a depth of no less than 1/4 of the concrete thickness, using a concrete cutter. This must be done within 24 hours. Contraction joints serve as load transfer devices, dividing the concrete into blocks every 4.5 meters to control cracking. After cutting, apply an asphalt sealant to the joint. As cracking occurs, the load on the concrete is transferred to the adjacent block. Finally, the forms can be carefully removed after 24 hours. Form Specifications: Use straight side forms made of metal (at least 7/32 inch thick) and at least 10 feet in length. Forms must be of sufficient depth and width to maintain alignment and withstand the weight of equipment without springing. 6. Testing and Surface Requirements Test Specimens: o Beam and Cylinder Preparation: Prepare test specimens according to AASHTO T 23 and cure them as specified for pavement testing. For every 75 cubic meters of concrete laid, beam samples must be taken for curing and subjected to a flexural test. The test results must meet or exceed the required strength. If the results are below the required strength, the contractor may face penalties, or the concrete may need to be removed. The beam dimensions should be 150mm x 1500mm x 525mm x 230mm (depth).  o Surface Trueness: Conduct straightedge testing within 14 days of placement to ensure surface trueness. The surface should not vary more than 0.25 inches from the straightedge. 7. Opening to Traffic Strength Requirement: The pavement should not be opened to traffic until test specimens indicate a flexural strength of 550 psi, with a minimum curing period of 7 days. Traffic Restrictions: Construction traffic and equipment should not be allowed on the pavement until it has achieved the required strength. 8. Measurement and Payment Measurement: o Concrete Pavement: Paid on a lump sum basis. Transverse contraction joints are measured per linear foot. o Core Sampling: The thickness of the pavement is determined by core samples. Pavement found to be deficient by more than 0.2 inches but less than 0.6 inches will result in a reduced payment. Payment Adjustments: o Thickness Deficiency: If the average pavement thickness is deficient by more than 0.2 inches, the payment will be adjusted according to Table 411-I. Areas deficient by more than 1 inch may not be paid for and may require removal and replacement. o Profile Index: Payment adjustments based on profile index range from 100% for an index of 10 or less, to required corrective work for an index over 15. Equipment Requirements Batching Plant and Mixers: o Compliance: Must conform to Section 601 - Structural Concrete. o Capacity and Mechanical Condition: Equipment must be capable of handling the required materials and in good mechanical condition. Hauling Equipment: o Compliance: Hauling equipment must also conform to Section 601 standards. Finishing Equipment: o Finishing Machine: Self-propelled, equipped with oscillating transverse screeds to handle and finish concrete. Must not displace reinforcement, side forms, or joints.  o Vibrators: Surface pan type or internal type (immersed tube or multiple spuds) with frequencies of: ▪ Surface Vibrators: Minimum 3,500 impulses per minute. ▪ Internal Vibrators: Minimum 5,000 impulses per minute. o Machine Floats: Self-propelled, designed to finish pavement smoothly and true to grade. o Slip-Form Pavers: Self-propelled, equipped with traveling side forms for spreading, consolidating, and screeding concrete. Must include high-frequency internal vibrators. Concrete Saw: o Sawing Equipment: Must be adequate in number and power, using water-cooled diamond edge saw blades or abrasive wheels for joint cutting. Ensure availability of backup saws and ample supply of blades. Forms: o Form Specifications: Use straight side forms made of metal (at least 7/32 inch thick) and at least 10 feet in length. Forms must be of sufficient depth and width to maintain alignment and withstand the weight of equipment without springing. Ang haba ng Tie (Deformed Bars) at Dowel Bars (Plain Round Bars) ay parehong 600mm. Pagdating naman sa bilang ng Tie at Dowel Bars ay mag dedepende sa magiging spacing nito halimbawa ang Tie Bar spacing ay 750mm, ibig sabihin sa isang span o block (4.5m) 4500mm/750mm= 6 pirasong Tie Bars ang magagamit. Gayun din naman para sa Dowel Bar depende sa magiging spacing, Material Quality Assurance The DPWH Blue Book outlines strict criteria for the materials used in PCCP to ensure that they meet the necessary standards for durability and strength. Cement: o Must comply with PNS or ASTM standards for Type I or Type II Portland cement. o Certification of cement quality is required from the supplier. Aggregates: o Coarse and fine aggregates must meet the requirements for gradation, cleanliness, and durability. o Coarse aggregates should be clean, hard, and free from deleterious materials, with specific size and gradation limits. o Fine aggregates should also be clean, with appropriate fineness modulus and grading. Water: o Potable water is preferred for mixing concrete. o Water should be free from impurities that could affect the strength and durability of the concrete. Admixtures: o Any chemical or mineral admixtures must be approved by the DPWH and must comply with relevant standards. 2. Concrete Mix Design and Approval Design Mix: o The contractor is required to submit a concrete mix design for approval before the start of construction. This mix design should achieve the specified compressive strength and workability. o The mix design process considers factors such as the water-cement ratio, aggregate sizes, and admixtures to achieve the required strength, durability, and workability. Trial Mixes: o Trial mixes must be conducted to verify that the proposed mix design will achieve the required properties. The DPWH may require tests such as the slump test and compressive strength test on these trial mixes. 3. Construction Practices The DPWH Blue Book specifies construction practices that must be followed to ensure the quality of the PCCP: Batching and Mixing: o Concrete must be mixed using approved equipment and procedures to ensure uniformity. Batching must be done by weight, not by volume, for accuracy. o The water-cement ratio should be strictly controlled, and the use of clean, quality- controlled aggregates is required. Transportation: o Concrete must be transported from the mixing plant to the site in such a way that prevents segregation and loss of materials. o Delivery times must be short enough to avoid any initial setting of the concrete before placement. Placing and Compaction: o The concrete must be placed and compacted within the time limits specified to avoid setting before compaction. o Adequate vibration should be used to remove air pockets and ensure a dense, uniform pavement. Curing: o Proper curing practices must be followed to prevent premature drying and ensure the concrete achieves its full strength potential. This includes maintaining  moisture levels for a specified period, usually by using water sprays, wet coverings, or curing compounds. 4. Testing and Inspection The DPWH Blue Book outlines mandatory testing and inspection procedures to verify that the constructed PCCP meets the required quality standards. Slump Test: o Conducted to ensure the workability of concrete during placement. The acceptable slump range is specified based on the type of work and conditions. Compressive Strength Test: o Concrete samples (usually cylinders or cubes) are taken during construction and cured under specified conditions. These samples are tested at 7, 14, and 28 days to ensure that the concrete meets the specified compressive strength. Thickness and Surface Regularity: o The thickness of the pavement must be checked at regular intervals to ensure compliance with the design specifications. o Surface regularity is inspected to ensure that the pavement surface is smooth and even, meeting the tolerances specified in the Blue Book. Quality Control Testing: o The contractor must conduct regular quality control tests as specified by the DPWH. This includes testing for air content, unit weight, and other properties as required by the project specifications. 5. Documentation and Compliance Quality Control Records: o All test results, inspection reports, and compliance records must be documented and submitted to the DPWH as part of the project’s quality assurance documentation. Non-Compliance and Remediation: o Any materials or construction practices that do not meet the Blue Book standards must be corrected. Non-compliant concrete may need to be removed and replaced at the contractor’s expense. 6. Final Acceptance Final Inspection: o Before final acceptance of the PCCP, a thorough inspection is conducted to ensure that all aspects of the pavement construction meet the DPWH Blue Book specifications. Certification: o The contractor must provide certification that the PCCP has been constructed according to the approved plans and specifications. Sub-grade Quality Assurance Definition: The sub-grade is the natural soil or improved soil on which the pavement structure is built. It provides foundational support to the layers above. Quality Assurance Procedures: Soil Investigation: o Conduct a thorough geotechnical investigation to determine the properties of the in-situ soil, including its bearing capacity, moisture content, and compaction characteristics. o Identify any problematic soil conditions such as expansive soils, high moisture content, or low bearing capacity that may require treatment or replacement. Compaction: o The sub-grade must be compacted to achieve the specified density, typically 95% of the Maximum Dry Density (MDD) as determined by the Proctor test. o Compaction is usually verified through field density tests using a nuclear density gauge or sand cone method. Moisture Control: o Ensure that the moisture content of the sub-grade is within the optimum range for compaction. Too much or too little moisture can affect compaction efficiency. o If the moisture content is too high, allow time for drying or use appropriate drying techniques. If it is too low, water may be added. Surface Preparation: o The sub-grade surface should be smooth, free of loose material, and graded to the required slope and elevation. This ensures proper drainage and a uniform foundation for the subsequent layers. o Conduct a proof rolling test to check for soft spots or areas of insufficient compaction. 2. Sub-base Quality Assurance Definition: The sub-base is an optional layer between the sub-grade and base course. It provides additional support and improves load distribution. Quality Assurance Procedures: Material Quality: o Ensure that the sub-base material meets the specified gradation and quality requirements, typically consisting of well-graded granular materials such as crushed stone, gravel, or stabilized soil. o Check for deleterious materials such as clay, silt, or organic matter that could weaken the layer.  Compaction: o The sub-base layer should be compacted to the specified density, typically around 100% of the Maximum Dry Density (MDD). o Conduct field density tests to verify compaction, ensuring that the layer is uniformly compacted across the entire area. Thickness Control: o Verify that the sub-base is constructed to the specified thickness. Regular checks using survey equipment should be conducted during placement. o Any deviations from the specified thickness should be corrected by adding or removing material. Moisture Control: o Similar to the sub-grade, the moisture content of the sub-base material must be controlled to achieve optimal compaction. Ensure moisture is within the optimum range before and during compaction. Surface Smoothness: o The surface of the sub-base should be smooth and level, providing a stable foundation for the base course. Irregularities should be corrected before placing the base course. 3. Base Course Quality Assurance Definition: The base course is a critical load-bearing layer directly under the pavement surface, typically composed of high-quality granular materials. Quality Assurance Procedures: Material Quality: o Use high-quality crushed aggregate, crushed stone, or crushed concrete that meets the gradation, durability, and strength requirements specified in the project specifications. o Regularly sample and test materials for compliance with specifications, including checking for deleterious materials. Compaction: o The base course must be compacted to a high density, often specified as 100% of the Maximum Dry Density (MDD). o Field density tests should be conducted frequently to ensure uniform compaction across the entire area. Gradation and Layer Thickness: o The material should be well-graded to ensure proper interlocking and load distribution. Regular gradation tests should be performed to verify compliance. o Ensure that the base course is placed and compacted in layers, with each layer not exceeding the specified maximum thickness, typically around 150mm. The total thickness should meet design specifications. Moisture Control: o Proper moisture content is essential for achieving maximum compaction. The moisture content should be maintained within the optimum range during placement and compaction. Surface Smoothness and Leveling: o The base course surface should be smooth, level, and free of any loose or segregated material. It should conform to the design grades and cross slopes specified in the project plans. o Survey the surface regularly during construction to ensure it meets the design elevation and smoothness criteria. Strength Testing: o Perform CBR (California Bearing Ratio) tests or Plate Load Tests to verify that the base course material provides the required support. o Conduct regular inspections to ensure that the base course meets the design strength criteria. Specifies the chemical and physical requirements for Portland cement used in concrete. This includes the composition, fineness, setting time, soundness, and strength requirements. Types of Portland cement covered include Type I (general purpose), Type II (moderate sulfate resistance), Type III (high early strength) Covers blended cements, which are made by intergrinding or blending Portland cement with supplementary cementitious materials like fly ash, pozzolan, or slag. Specifies the quality and grading of fine and coarse aggregates. -Includes requirements for particle size distribution, shape, texture, cleanliness (limits on deleterious materials like silt, clay, and organic impurities), and strength. -Guidelines include the proportioning of materials (cement, water, aggregates, and admixtures) to produce a concrete mix that meets the desired properties. Emphasizes testing of trial mixes and adjustments to achieve the target strength and consistency. -Low Workability (0-25mm): Suitable for road construction or where compaction by vibration is required. -Medium Workability (25-50mm): Used for most general construction purposes, including residential buildings. -High Workability (50-100mm): Appropriate for heavily reinforced structures, columns, and beams. Concrete Specimens: Typically, concrete cubes or cylinders are used. The common sizes are: Cubes: 150mm x 150mm x 150mm. Cylinders: 150mm diameter and 300mm height. Types of Proctor Tests 1. Standard Proctor Test (ASTM D698): o Used for light compaction, typically in applications like residential buildings or lightweight pavements. o Involves compacting soil in three layers, each with 25 blows from a 5.5-pound (2.5 kg) hammer dropped from a height of 12 inches (305 mm). 2. Modified Proctor Test (ASTM D1557): o Used for heavy compaction, usually for more critical infrastructure projects like highways, airports, and heavy-duty pavements. o Involves compacting soil in five layers, each with 25 blows from a 10-pound (4.54 kg) hammer dropped from a height of 18 inches (457 mm). Methods of Air Content Testing There are two common methods for testing the air content of freshly mixed concrete: 1. Pressure Method (ASTM C231): o Most widely used for PCCP. o Suitable for concrete with dense aggregates (no lightweight aggregates). o Measures the change in pressure within a chamber to determine air content. 2. Volumetric Method (ASTM C173): o Suitable for all types of aggregates, including lightweight. o Measures air content by displacing air in the concrete with water. o Requires more effort and time compared to the pressure method. Procedure for the Pressure Method (ASTM C231) Here’s an outline of the steps involved in the pressure method: 1. Sample Preparation: o Collect a sample of freshly mixed concrete. o Fill the measuring bowl of the air meter in three layers, compacting each layer with a tamping rod (25 strokes per layer). 2. Strike Off and Seal: o After filling the bowl, strike off the excess concrete to achieve a smooth, level surface. o Attach the top section of the air meter to the bowl and secure it tightly to ensure an airtight seal. 3. Pressurization: o Fill the air chamber with water to remove any air above the concrete. o Open the valves on the air meter to equalize the pressure and then close them. o Apply pressure by pumping the air meter until the gauge reads the calibrated pressure level. 4. Measure Air Content: o Release the pressure, and the gauge will indicate the air content percentage directly. o Record the reading. 5. Correction and Reporting: o If necessary, apply correction factors for the specific concrete mix or temperature. o Report the air content as a percentage of the total volume of concrete. Procedure for the Volumetric Method (ASTM C173) The volumetric method involves slightly different steps: 1. Sample Preparation: o Collect and place the concrete sample in a calibrated container. o Add water to fill the container, eliminating any trapped air. 2. Agitation: o Shake and agitate the container to release air bubbles from the concrete. o The container is typically inverted and rolled to ensure all trapped air escapes. 3. Measurement: o After agitation, allow the container to sit until the liquid stabilizes. o The change in volume (read from the calibrated container) corresponds to the air content. Interpreting Results Ideal Air Content: Typically ranges from 4% to 8% depending on the environmental conditions and type of concrete. Adjustment: If the air content is too high or too low, adjustments to the mix (e.g., adjusting the amount of air-entraining agent) may be required. Importance in PCCP Freeze-Thaw Resistance: Proper air content ensures the pavement can withstand cycles of freezing and thawing without significant damage. Workability and Finishability: Optimal air content contributes to better placement and finishing of the concrete. Longevity: Concrete with the correct air content is more durable, reducing the need for repairs and extending the life of the pavement. Importance of ASTM C138 Quality Control: Helps in verifying that the concrete mix meets the design specifications. Uniformity: Ensures consistency across different batches, reducing variability in the concrete's properties. Durability: Proper air content and density contribute to the concrete's resistance to environmental factors and longevity. Applications Used in field and laboratory settings to verify concrete quality. Particularly important in large projects like bridges, highways, and pavements, where uniformity and durability are critical.