Absorption Tests
Description
Absorption testing is a popular method of determining the water tightness. A water absorption test, such as BS 1881-122:2011 is a test that measures the amount of water that penetrates into concrete samples when submersed. Low absorption is considered a positive result.
Where it’s Most Useful
The Absorption test method is intended to determine the susceptibility of an unsaturated concrete to the penetration of water, for both the concrete surface and interior concrete.
Limitations
This test does have some inherent limitations including:
Short time duration of submersion compared to potential long term service conditions;
Does not account for any type of reactive process that ties up water; and
Assumes all weight gain is water and not reactive processes.
Can be misleading when it comes to the use of admixtures, such as hydrophilic crystalline waterproofing admixtures. Absorption testing measures the amount of water that penetrates into concrete samples when submersed, but fails to take into account the inherent use of water in the crystallization process, particularly in the early stages of curing (less than 28 days)*.
*The absorption test results will improve over time—as the concrete is saturated and crystals continue to grow. Therefore, in the case of crystalline admixtures, testing the absorption at later ages such as 56 or 90 days will give more realistic results.
RCP testRapid Chloride Permeability Test
Description
The Rapid Chloride Permeability (RCP) test is the standard test method for electrical indication of concrete’s ability to resist chloride ion penetration. Test methods—such as ASTM 1202, Standard Test Method for Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration—consists of monitoring the amount of electrical current passed through cylindrical specimens for a duration of six hours. The total charge passed, in coulombs, is found with the results relating to the resistance of the sample specimen to chloride ion penetration.
Where it’s Most Useful
The RCP test has gained wide acceptance as a relatively easy and quick method for determining concrete permeability. Overall, as per ASTM, this test method is suitable for the evaluation of materials and material proportions for design purposes, and for research and development. However, it has incorrectly become one of the tests used to evaluate the durability of concrete. RCP can qualify a mix, but not necessarily disqualify it.
The RCP test should not be used to accurately determine the permeability of a concrete mix containing supplementary cementitious materials or chemical admixtures.
Limitations
This test does have various drawbacks that make it unreliable, especially for the comparison of different mix designs or for evaluating concrete durability.
Some of these limitations are:
It may allow for premature measurements (before a steady state is achieved);
High voltage applied leads to an increase in temperature to the sample, and can cause physical and chemical changes resulting in unrealistic values;
Electric current that passes through the sample during the test, indicates the movement of not just chloride ions, but all ions in the pore solution (the sample’s electrical conductivity); therefore, this test may not represent the true permeability (or potential permeability) for concrete that contains supplementary cementitious materials (e.g. fly ash, silica fume, or ground granulated blast-furnace slag) or chemical admixtures (e.g. water reducers, superplasticizers, or corrosion inhibitors);
There can be misleading results largely due to the chemical composition of the pore solution, rather than from the true permeability;
Concrete resistivity, rather than permeability, is measured—resistance is calculated as volts divided by current and it has been shown there is a fair correlation between concrete resistivity and concrete permeability, but it is not the intended use of the RCP test; and
The test has low inherent repeatability and reproducibility.
DIN 1048 Test
DIN 1048 Part 5 Permeability Test Method
Water Permeability Test
Description
BS EN 12390-8, Testing hardened concrete: Depth of penetration of water under pressure, and DIN 1048 Part 5, Testing concrete; testing of hardened concrete, water permeability, are equivalent tests which measure the depth of water penetration into concrete samples subjected to 0.5 MPa (72.5 psi) of hydrostatic pressure over a period of three days. Concrete specimens are cast and cured for 28 days. After curing, samples are then placed in the testing device. The sample holders are open at both ends, with one end subjected to hydrostatic pressure. After three days, the samples are removed from the testing apparatus and cracked in half vertically. The maximum depth of water penetration into the sample is then measured.
Where it’s Most Useful
These tests determine the true permeability of concrete by evaluating the resistance of concrete against the penetration of water under hydrostatic pressure. A permeability test should be considered the dominant test to evaluate the case whereby concrete is subjected to hydrostatic pressure.
When analyzing the results, the smaller the depth of penetration results in a higher resistance to water under hydrostatic pressure. This test method is useful for structures such as basements, tunnels, and water reservoirs because it recreates the pressure conditions these structures are subjected to in a realistic way.
Limitations
In spite of many advantages, like other tests, this test method has some limitations, such as:
For a dense and low permeable mix, the depth of water penetration is low, making it difficult to compare the mixes that have low permeation (for these cases the pressure or testing age can be modified); and
Evaluating cases in which the concrete is not under hydrostatic pressure, this test method should be considered as an auxiliary test method and tests such as absorption
对比混凝土耐久性测试方法
吸收测试
吸收测试是一个受欢迎的水密度的确定方法。吸水试验,如BS 1881 - 122:2011测试水渗透情况，当浸没混凝土样品时。低吸收被认为是一个积极的结果。
最有用的的方面
吸收测试方法的目的是确定渗透水对不饱和混凝土的敏感性,对于混凝土表面和内部混凝土。
局限
这个测试有一些固有的局限性包括:
短时间淹没和潜在的长期作用条件情况下的比较;没有考虑到任何锁水的反应过程。假设所有的体重增加是水,而不是被动的过程。外加剂的使用可以导致误导,如亲水结晶防水外加剂。吸收测试方法的水渗透到混凝土样本浸没时,但未能考虑到水在结晶过程中,特别是在早期阶段的养护(少于28天)*。*吸收测试结果将在那次混凝土饱和和提高晶体继续增长。因此,在水晶掺合料的情况下,测试等吸收在后世56或90天将给更现实的结果。
RCP testRapid氯化物渗透性测试
快速氯离子渗透测试(RCP)是电的标准测试方法表明混凝土抵抗氯离子渗透的能力。测试ASTM 1202,电气测试方法标准的混凝土抗氯离子的能力Penetration-consists监测电流6个小时的时间通过圆柱标本的量。通过的总电荷、库伦,结果发现有关样品的氯离子渗透。
最有用的的方面
RCP测试获得了广泛接受作为一个相对容易和快速确定混凝土渗透性的方法。按ASTM,总体而言,这种测试方法适用于评估的材料和材料的比例设计的目的,以及研究和开发。然而,它错误地成为了测试用于评估混凝土的耐久性。RCP可以晋级,但不一定取消它。
RCP测试不应被用来精确确定的渗透率包含辅助胶结材料或化学外加剂的混凝土混合物。
限制
这个测试有各种缺点,这些缺点使它不可靠,特别是对比较不同的混合设计或评价混凝土耐久性。
这些限制包括:
这可能允许过早测量(在达到稳定状态(前);高电压导致样品温度的增加,会导致物理和化学变化导致不切实际的值;电流通过样品在测试期间,表明不仅仅是氯离子的运动,但孔隙中所有离子解决方案(样品的导电性);因此,这个测试可能不代表真正的渗透率(或潜在的渗透率)混凝土包含补充胶结材料(如粉煤灰、硅灰、或地面粒状高炉矿渣)或化学外加剂(例如水还原剂、superplasticizers或缓蚀剂);可以有误导的结果很大程度上是由于孔隙溶液的化学成分,而不是真正的渗透率;混凝土电阻率,而不是渗透率,measured-resistance计算电压除以电流,它已被证明有一个公平的混凝土电阻率和混凝土渗透率之间的关系,但这并不是预期的使用RCP测试;和
测试低固有的重复性和再现性。
DIN 1048测试
DIN 1048第5部分渗透试验方法
水渗透试验
BS EN 12390 - 8,测试硬化混凝土:深度渗透水压力,和DIN 1048第5部分,测试混凝土;测试硬化混凝土的透水性,是等价的测试测量水的深度渗透混凝土样品受到0.5 MPa(72.5 psi)的静水压力在一段时间内三天。混凝土标本是28天的演员和治愈。固化后,样品被放置在测试设备。样品持有人是开放的两端,一端受到静水压力。三天后,样品的测试装置和垂直了一半。水渗透到样本的最大深度测量。
这些测试确定真正的混凝土的渗透性评价混凝土的抗渗透静水压力下的水。应该考虑渗透率测试主要测试评估,混凝土受静水压力。
在分析结果时,渗透深度越小静水压力下导致更高的耐水性。这个测试方法是有用的结构如地下室、隧道和水库,因为它再现了这些结构压力条件受到现实的方式。
限制
尽管有很多优点,像其他的测试,这个测试方法有一定的局限性,如:密度和低渗透混合,水渗透的深度较低,很难比较低渗透的混合(这些情况下的压力或测试年龄可以修改);和评估具体的情况不是在静水压力下,该测试方法应考虑作为辅助测试方法和测试吸收等主导测试。
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