地下室水泥墙基这么烂，质量问题有多严重？
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http://www.forconstructionpros.com/article/11465408/visible-pour-lines-are-they-a-problem
Question: A recent project we were completing was held up when our homeowner ventured to the site to see the concrete work we had just unveiled during stripping of the forms. Across one wall was a visible line we commonly know to be a pour line but immediately the concern was “my foundation is already cracked,” what can we do to reassure our customer? – Concrete Contractor (Indiana)
Answer: We will agree that this is a very common inquiry that we receive from the market. Occasionally the contractor defending their work brings it to our attention and sometimes it is by the customer looking for third party assistance in either challenging the work or relieving their concern. Regardless of the purpose or direction for the inquiry, the reality is that blemishes and visible record of concrete placement is a natural part of the cast-in-place process, particularly when higher aesthetic standards or specifications are not set for the project.
The vast majority of the occurrences for these diagonal lines in a cast-in-place are the indication of a change in concrete load during placement. When a contractor is placing concrete in vertical formwork, regardless of the placement mechanism (e.g. concrete pump, conveyor or direct chute), the truck placing the concrete will run dry and a change is made. Concrete trucks traditionally carry between 7 and 10 cubic yards of concrete while an average 3,200 square-foot house foundation requires between 50 and 60 cubic yards of concrete.
Most residential lots have considerable restrictions on the movement of vehicles due to lot lines and other congestions, therefore only one truck at a time is able to deliver its load. When one finishes and moves out, the next moves in and placement resumes. Depending on the amount of time between starting and stopping, the concrete in the forms has already been vibrated by the crew waiting on the placement to resume. As the new load is placed, the contractor will resume vibrating the fresh concrete but may not extend the vibrators fully between the previous placement and the new concrete. This results in what the industry refers to as a “pour line” or a slight variation of color or texture that may indicate a natural color variation in the concrete, a different rate of compaction or vibration and most likely the difference in hydration stage of the fresh concrete.
Concrete begins hydrating the moment mixing begins of the cementitious particles and water. There are multiple stages or benchmarks for the hydration process that range from mixing to initial set, final set to design strength, etc. The contractor should fully recognize the stages of workability and to make certain that initial set is not reached between placements. If this happens, rather than a “pour line” between concrete placements, a “cold joint” will occur. A cold joint is where the previous placement hardens prior to the receipt of the next placement and the result may be a reduction of the monolithic behavior for the concrete element, in this case a foundation wall.
Professional concrete contractors can easily identify if the concern for a cold joint is present and can plan to remediate the problem should that occur before they start the next placement. However, should a serious concern exist for a cold joint over a pour line, there are non-destructive methods to core and examine the concrete before making the final determination of the best way to proceed.
Wall sections that have cold joints and steel reinforcement are likely to still perform adequately due to the combination of shear transfer across the joint due to the steel reinforcement bars and the coefficient of friction at the rough joint. An engineer may also review the joint if sufficient concern exists.
ACI 309.2R-98 – Identification and Control of Visible Effects of Consolidation on Formed Concrete
Question: A recent project we were completing was held up when our homeowner ventured to the site to see the concrete work we had just unveiled during stripping of the forms. Across one wall was a visible line we commonly know to be a pour line but immediately the concern was “my foundation is already cracked,” what can we do to reassure our customer? – Concrete Contractor (Indiana)
Answer: We will agree that this is a very common inquiry that we receive from the market. Occasionally the contractor defending their work brings it to our attention and sometimes it is by the customer looking for third party assistance in either challenging the work or relieving their concern. Regardless of the purpose or direction for the inquiry, the reality is that blemishes and visible record of concrete placement is a natural part of the cast-in-place process, particularly when higher aesthetic standards or specifications are not set for the project.
The vast majority of the occurrences for these diagonal lines in a cast-in-place are the indication of a change in concrete load during placement. When a contractor is placing concrete in vertical formwork, regardless of the placement mechanism (e.g. concrete pump, conveyor or direct chute), the truck placing the concrete will run dry and a change is made. Concrete trucks traditionally carry between 7 and 10 cubic yards of concrete while an average 3,200 square-foot house foundation requires between 50 and 60 cubic yards of concrete.
Most residential lots have considerable restrictions on the movement of vehicles due to lot lines and other congestions, therefore only one truck at a time is able to deliver its load. When one finishes and moves out, the next moves in and placement resumes. Depending on the amount of time between starting and stopping, the concrete in the forms has already been vibrated by the crew waiting on the placement to resume. As the new load is placed, the contractor will resume vibrating the fresh concrete but may not extend the vibrators fully between the previous placement and the new concrete. This results in what the industry refers to as a “pour line” or a slight variation of color or texture that may indicate a natural color variation in the concrete, a different rate of compaction or vibration and most likely the difference in hydration stage of the fresh concrete.
Concrete begins hydrating the moment mixing begins of the cementitious particles and water. There are multiple stages or benchmarks for the hydration process that range from mixing to initial set, final set to design strength, etc. The contractor should fully recognize the stages of workability and to make certain that initial set is not reached between placements. If this happens, rather than a “pour line” between concrete placements, a “cold joint” will occur. A cold joint is where the previous placement hardens prior to the receipt of the next placement and the result may be a reduction of the monolithic behavior for the concrete element, in this case a foundation wall.
Professional concrete contractors can easily identify if the concern for a cold joint is present and can plan to remediate the problem should that occur before they start the next placement. However, should a serious concern exist for a cold joint over a pour line, there are non-destructive methods to core and examine the concrete before making the final determination of the best way to proceed.
Wall sections that have cold joints and steel reinforcement are likely to still perform adequately due to the combination of shear transfer across the joint due to the steel reinforcement bars and the coefficient of friction at the rough joint. An engineer may also review the joint if sufficient concern exists.
ACI 309.2R-98 – Identification and Control of Visible Effects of Consolidation on Formed Concrete
感觉这个不只是“Pour Line"的问题吧 ？
这个部分 感觉粉碎性的，感觉水泥不行，不solid，好像不是 气泡的问题 ，是水泥质量的问题，或者是杂质太多，感觉像是和泥土 混在一起了 。。。
行家请 仔细看看照片，是不是 ？
这个部分 感觉粉碎性的，感觉水泥不行，不solid，好像不是 气泡的问题 ，是水泥质量的问题，或者是杂质太多，感觉像是和泥土 混在一起了 。。。
行家请 仔细看看照片，是不是 ？
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The primary difference between concrete and cement is that concrete is a composite material made of water, aggregate, and cement. Cement is a very fine powder made of limestone and other minerals, which absorbs water and acts as a binder to hold the concrete together. While cement is a construction material in its own right, concrete cannot be made without cement. The two terms often are incorrectly used interchangeably, but concrete and cement are distinctly separate products.
Cement
Cement is made from limestone, calcium, silicon, iron, and aluminum, among other ingredients. This mixture is heated in large kilns to about 2,700°F (1,482°C) to form a product known as clinkers, which roughly resemble marbles. These are ground into a powder and gypsum is added, creating the gray flour-like substance known as cement. When water is added to cement, it triggers a chemical process that allows it to harden.
Portland Cement
There are many different types of cement, but the type most commonly used in construction is Portland cement. Joseph Aspdin of Britain developed the building material in the 1700s, when he found that adding clay to limestone and superheating the mixture allowed the resulting blend to set anywhere. Portland cement is a type of hydraulic cement, which means that when water is added, it starts a chemical reaction that is not dependent on how much water there is. This allows the cement to harden underwater and remain strong even in wet conditions. The different types of hydraulic cement are primarily used in concrete and mortars.
Concrete
Concrete, in contrast, is a masonry material that uses cement to bind together crushed stone, rock, and sand, also called aggregate. Cement makes up from 10% to 15% of the total mass of concrete; the exact proportions vary depending on the type of concrete being made. The aggregate and cement are mixed thoroughly with water, which starts the chemical reaction causing the cement to harden and set. Before this happens, the concrete mix can be poured into a mold so that it will harden in a specific shape, be it a block or a slab.
The amount of time it takes for concrete to set depends in part on how much gypsum is added to the mixture. This time can be accelerated by adding calcium chloride or slowed by adding sugar. These compounds work by affecting the development of the hardening crystals that form as concrete sets. Concrete that is exposed to freezing and thawing conditions may have additional chemicals added to help prevent cracking.
Concrete and Cement Ratios
The properties of concrete depend a great deal on the ratio of aggregate-to-cement-to-water in the mix. The water-to-cement ratio is the most important, as too little water will make the concrete mix difficult to work with, while too much will weaken the final product. This ratio is calculated with the following equation:
In this calculation, r is the ratio, qH2O is the quantity of water in US gallons, and Wc is the weight of cement in pounds. A ratio of at least 0.25 is required for concrete to harden, while values of 0.35 to 0.4 are typical for most applications.
Aggregate is also important, as it makes up more than 60% of a concrete mix — and up to 80% in some cases. Larger rocks require less concrete, which means less water is needed, and a stronger final product can be made. Aggregate is also less expensive than cement, so a higher percentage can lower the cost. Generally speaking, a good aggregate has a combination of rocks of many different sizes, with a specific average and maximum size; these stones must be clean and durable, and should not contain clay or other minerals that can absorb water.
Concrete's high rock content makes it extremely durable, and it often is used in swimming pool decking, skyscrapers, subways, and lamp posts, as well as sidewalks, driveways, and roads. The ingredients in both concrete and cement are among the most abundant on Earth, and both can be recycled. Cement production does require a large amount of energy, however, because of the high temperatures required and the industry has been criticized for its contributions to carbon dioxide emissions.
Cement
Cement is made from limestone, calcium, silicon, iron, and aluminum, among other ingredients. This mixture is heated in large kilns to about 2,700°F (1,482°C) to form a product known as clinkers, which roughly resemble marbles. These are ground into a powder and gypsum is added, creating the gray flour-like substance known as cement. When water is added to cement, it triggers a chemical process that allows it to harden.
Portland Cement
There are many different types of cement, but the type most commonly used in construction is Portland cement. Joseph Aspdin of Britain developed the building material in the 1700s, when he found that adding clay to limestone and superheating the mixture allowed the resulting blend to set anywhere. Portland cement is a type of hydraulic cement, which means that when water is added, it starts a chemical reaction that is not dependent on how much water there is. This allows the cement to harden underwater and remain strong even in wet conditions. The different types of hydraulic cement are primarily used in concrete and mortars.
Concrete
Concrete, in contrast, is a masonry material that uses cement to bind together crushed stone, rock, and sand, also called aggregate. Cement makes up from 10% to 15% of the total mass of concrete; the exact proportions vary depending on the type of concrete being made. The aggregate and cement are mixed thoroughly with water, which starts the chemical reaction causing the cement to harden and set. Before this happens, the concrete mix can be poured into a mold so that it will harden in a specific shape, be it a block or a slab.
The amount of time it takes for concrete to set depends in part on how much gypsum is added to the mixture. This time can be accelerated by adding calcium chloride or slowed by adding sugar. These compounds work by affecting the development of the hardening crystals that form as concrete sets. Concrete that is exposed to freezing and thawing conditions may have additional chemicals added to help prevent cracking.
Concrete and Cement Ratios
The properties of concrete depend a great deal on the ratio of aggregate-to-cement-to-water in the mix. The water-to-cement ratio is the most important, as too little water will make the concrete mix difficult to work with, while too much will weaken the final product. This ratio is calculated with the following equation:
In this calculation, r is the ratio, qH2O is the quantity of water in US gallons, and Wc is the weight of cement in pounds. A ratio of at least 0.25 is required for concrete to harden, while values of 0.35 to 0.4 are typical for most applications.
Aggregate is also important, as it makes up more than 60% of a concrete mix — and up to 80% in some cases. Larger rocks require less concrete, which means less water is needed, and a stronger final product can be made. Aggregate is also less expensive than cement, so a higher percentage can lower the cost. Generally speaking, a good aggregate has a combination of rocks of many different sizes, with a specific average and maximum size; these stones must be clean and durable, and should not contain clay or other minerals that can absorb water.
Concrete's high rock content makes it extremely durable, and it often is used in swimming pool decking, skyscrapers, subways, and lamp posts, as well as sidewalks, driveways, and roads. The ingredients in both concrete and cement are among the most abundant on Earth, and both can be recycled. Cement production does require a large amount of energy, however, because of the high temperatures required and the industry has been criticized for its contributions to carbon dioxide emissions.
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Cold Joints
Description
Cold joints are formed primarily between two batches of concrete where the delivery and placement of the second batch has been delayed and the initial placed and compacted concrete has started to set. The full knitting together of the two batches of concrete under vibration to form a homogeneous mass is therefore not possible, unlike the compaction of two fresh workable batches of concrete. This could be a potential plane of weakness.
Cold joints, unlike cracks that form in hardened concrete through tensile restraint, are not gaps in the concrete but merely seams containing no appreciable void structure. They are usually linear, closely joined and bonded. However, there is a danger of small voids in areas where the concrete is not fully compacted, as with any concrete pour.
Generally, cold joints are not a problem structurally if the joint is in compression. However, the location of the joint within the structure, the structural function of the element and aesthetics need to be considered when assessing a cold joint.
concrete cold pouring joint可能会造成以后渗水。
Description
Cold joints are formed primarily between two batches of concrete where the delivery and placement of the second batch has been delayed and the initial placed and compacted concrete has started to set. The full knitting together of the two batches of concrete under vibration to form a homogeneous mass is therefore not possible, unlike the compaction of two fresh workable batches of concrete. This could be a potential plane of weakness.
Cold joints, unlike cracks that form in hardened concrete through tensile restraint, are not gaps in the concrete but merely seams containing no appreciable void structure. They are usually linear, closely joined and bonded. However, there is a danger of small voids in areas where the concrete is not fully compacted, as with any concrete pour.
Generally, cold joints are not a problem structurally if the joint is in compression. However, the location of the joint within the structure, the structural function of the element and aesthetics need to be considered when assessing a cold joint.
concrete cold pouring joint可能会造成以后渗水。
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