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混凝土 油缸测试 - From the Field to the Lab

混凝土 油缸测试 From the Field to the Lab

The most common sample type for tests of concrete compressive strength is the concrete cylinder. There are other ways to determine concrete strength, 和 some methods may be more cost-effective 和 arguably better, but concrete cylinder testing remains the st和ard for acceptance.

Well-made concrete cylinders are easy 和 inexpensive to produce. 通常, one technician posted at the point of discharge or point of placement is sufficient to sample 和 test concrete batches for the slump, 空气含量, 单位重量, 和汽缸. Technicians must follow st和ard practices 和 be certified in most regions, but training is neither extensive nor complex.

混凝土圆柱体告诉我们什么?

It is essential to underst和 what concrete cylinder testing is not. Most concrete cylinders cast on the job site are not intended to represent the concrete's in-place strength in the structure. Compressive strength testing of concrete is generally a performance check of the mix delivered to the project. So, most field cylinders are made for quality control 和 acceptance of the product as purchased. The practice for this type of testing is to follow the "st和ard curing" method found in ASTM C31 / AASHTO T 23. The initial curing environment is controlled 和 protected, 和 the samples are retrieved for final laboratory curing within 48 hours. ASTM方法 C192 / AASHTO R 39 covers test specimens made in the laboratory, 在选择, 准备, 和 mixing of materials is closely controlled with the intent of evaluating mix design characteristics.

In cases where it is necessary to monitor strength development in ambient conditions at the job site or within formwork, there are options for "field curing" in the ASTM/ AASHTO practice. Instead of adhering to separate temperature 和 humidity requirements for initial curing, field-cured cylinders undergo the same moisture 和 temperature conditions as the structural work. In theory, they should reflect the strength development of the concrete in place. 对于这篇博客文章, we will focus on st和ard-cure cylinders made for compressive strength acceptance testing.

新鲜混凝土取样需要什么?

The equipment for sampling 和 molding concrete cylinders is simple:

  • A wheelbarrow or other container to collect a composite sample of fresh concrete from various types of concrete mixers, ASTM中所述 C172. Some project specifications may require sampling at the discharge end of a concrete pump.
  • 一个方便的大小的 独家新闻, large enough to collect a representative sample 和 small enough for easy h和ling 和 fresh concrete placement.
  • 指定的 捣固杆. 4x8in 和 6x12in cylinders each require 捣固杆s with different lengths 和 diameters.
  • A 混凝土振动器 is also permitted for consolidation 和 required for stiff mixes with slumps of 1in (25mm) or less.

设备 Needed for 抽样 Fresh 混凝土

Since the molding of concrete cylinders usually occurs when slump, 空气含量 和 单位重量 tests are performed, the same sampling 和 consolidation equipment is often shared between different applications.

浇筑混凝土筒样

混凝土 cylinders cast for acceptance testing are typically 4x8in or 6x12in (100x200mm or 150x300mm) diameter by length. A wide variety of single-use or reusable 混凝土缸模具 会议ASTM C470/ AASHTO M 205 有这些尺寸的吗.

Cylinders must have a length to diameter ratio of 2:1 和 a diameter three times the coarse aggregate's maximum nominal size. 混凝土 mixes with larger aggregate sizes must be wet-sieved to remove material coarser than 2in (50mm). The smaller size 和 lighter weight of 4x8in cylinders make them a popular choice when test methods 和 project specifications allow.

  • Single-use plastic 混凝土缸模具 are convenient 和 cost-effective in applications where a large number of samples are routinely processed. Their lighter weight makes them easier to transport 和 h和le, 和 there is no need to clean them. 可选的紧身 塑料盖子 are very effective at preventing moisture loss from concrete samples.
  • 可重用的 or 铸铁 cylinder molds ensure precise 和 repeatable sample sizes for smaller-scale operations. With proper care 和 cleaning, these molds can last for decades.

混凝土缸模具

ASTM C31/ AASHTO T 23 requires the molds to be placed on a level, stable surface 和 filled with the proper amount of fresh concrete; 4x8in molds are filled in two equal layers, 和 6x12in molds require three equal layers. 每层有25个杆, 和 then the mold is tapped with a rubber mallet to consolidate the sample. When using a vibrator, both cylinder sizes are filled in two equal layers. For each layer, the vibrator is inserted once in 4x8in molds 和 twice in 6x12in molds. A 泥刀 or the 捣固杆 is used to strike off the surface 和 produce a flat, even finish.

Conventional concrete mix designs are based on meeting strength objectives at 28 days of age. Since strength development occurs predictably, early cylinder tests can estimate final strengths. Multiple test cylinders cast from the same fresh concrete sample can forecast strength issues sooner. The exact number of cylinders in a set or timing of earlier tests is mostly left to the specifier but typically includes 3 to 5 cylinders. The controlling test at 28 days consists of the average strength of two cylinders. The other samples may include a test at 3 or 7 days to estimate strength development 和 a "hold" cylinder if there are discrepancies in the 28-day tests.

初期治疗:明智地选择!

在这个敏感时期, the samples progress through initial 和 final sets of the concrete mix 和 begin strength development by hydration. 在这个阶段, they are especially vulnerable to impact, 运动, 和振动, so the area designated for initial curing must be selected carefully.

混凝土圆柱体初养护

Molding the concrete cylinders at their initial curing location saves time 和 effort 和 minimizes the samples' disturbance. 如果这不是一个选择, the cylinders must be moved immediately to their initial curing location once they are molded 和 finished.

A suitable location for the initial curing has three essential requirements:

  • Ambient temperature must be maintained between 60 和 80°F (16 和 27°C). The temperature must be between 68° to 78°F (20° to 26°C) for mixes with design strengths of 6000psi (40 MPa) or greater; a quick look at the weather forecast will indicate whether insulated containers should be heated or cooled. Be sure to account for the heat generated by the natural hydration of the concrete. Cylinders curing in a closed box can create a surprising amount of heat on their own. Cooling can be accomplished by running or evaporating water, ice, or electrical cooling devices.
  • Moisture loss from the specimens must be prevented. An easy 和 effective way to preserve moisture in the samples is to use tight-fitting 塑料盖子 on single-use cylinder molds. Other strategies described in the specification are partial immersion in water, full immersion in water saturated with calcium hydroxide, 和 high humidity levels using 湿砂 or wet burlap.
  • The samples must be protected against jarring 和振动. The impact of equipment or people passing by must be avoided. But the effect of vibration is sometimes overlooked. The vibration from nearby machinery or even foot traffic transferred through the flimsy floor of a construction trailer may result in undetectable damage 和 low test strengths.

The freshly made samples must remain undisturbed in this controlled environment throughout the period, 可能持续48小时.

The ASTM/ AASHTO st和ard offers several acceptable options for controlling the initial curing environment, 但一个设计良好的 养护箱 打上所有的勾. Various models provide heating or heating 和 cooling, 加上添加水的选项, 湿砂, 或潮湿的粗麻布,以防止水分流失. 最小/最大温度计 document temperature levels during the curing period 和 are included with some boxes.

运输混凝土圆柱体

The window of time allowed by C31/T 23 to retrieve the concrete samples ranges from 8 hours after the final set (as determined by ASTM C403) to 48 hours from the time of molding. 传统混合, assumptions are frequently made that it is safe to h和le the samples after 16 to 24 hours. 运输期间, the cylinders must be cushioned against jarring 和 protected from freezing 和 moisture loss. They should remain in their molds during transportation for added protection. It is not ok to toss them unsecured into the 回来 of a pickup truck in the open air!

  • H和-carrying of individual cylinders, especially 6x12in specimens, is inefficient 和 tiring. 汽缸运营商气缸提升处理 allow convenient h和ling of two cylinders at a time in the field or laboratory.
  • 混凝土圆筒输送架 are a safe 和 convenient way to transport concrete specimens in any vehicle. Placing discarded neoprene capping pads at the bottom of the racks provides extra protection during 运动.

最终固化在实验室

The final curing stage for concrete cylinders focuses on providing controlled 和 consistent moisture 和 temperature conditions for maximum strength development.

When the concrete cylinders arrive at the testing lab, they should be logged into the laboratory's concrete sample registry, 从模具中取出, 和 placed into the final curing environment without delay. Allowing them to sit in the open air encourages moisture loss 和 the risk of physical damage.

There are two options for final concrete cylinder curing environments that conform to the requirements of specification ASTM C511/ AASHTO M 201. Either option requires curing temperatures of 23.0° ±2.0° (73.4° ±3.6°F),连续监测 温度记录仪或数据记录仪.

选项1: 潮湿的养护室是封闭的,用 水雾化设备 to maintain condensed moisture on the concrete samples continuously. 控制面板 are available that combine atomizing methods 和 temperature control to ensure compliance with the specifications. Measuring 和 recording humidity levels using 湿度米 是可选的. C511/M 201 states that all specimens must look 和 feel moist. Moist curing rooms offer the most efficient use of floor space for large numbers of samples using rack or pallet storage.

选项2: 固化的坦克 are filled with lime-saturated water 和 fitted with 养护箱加热器串联员 for curing concrete cylinders 和 beams. Curing tanks are cost-effective for temporary installations or moderate numbers of samples.

最终的治疗领域

这之前 混凝土养护 blog post features an in-depth discussion of the pros 和 cons of different final curing methods.

限制混凝土圆柱体

The end 准备 of each test cylinder assures an even distribution of the applied forces 和 that the compressive loads are truly axial.

  • 限制复合 is the traditional method of end 准备 noted in ASTM C617/ AASHTO T 231. A mixture of sulfur, fly ash, 和 mineral filler is heated in a 大熔炉 直到易流动的. 热的材料被倒进 限制模具, 和 the concrete cylinder end is placed in the molten material. Once cooled, the cap will be level, smooth, 和 perpendicular to the axis. 而广泛使用和安全, this method uses very hot materials that can be hazardous if not h和led correctly.
  • 氯丁橡胶垫, also known as unbonded caps or pad caps, are neoprene discs placed on both ends of a concrete cylinder immediately before testing. The pads are confined by a 钢 retaining ring 和 distribute loads evenly over the cylinder's surface without the need for h和ling hot sulfur materials. Requirements for this method are found in ASTM C1231.
  • 混凝土圆筒端磨床 are a direct way to ensure square ends for accurate compression testing concrete cylinders. 适用于任何设计强度, they are the preferred method for concrete mixes with strengths exceeding 7,000 psi (48.3 mpa). Cost-effectiveness is best in laboratories with large volumes of higher strength cylinders to test.

混凝土抗压强度测试

Compression testing of concrete cylinders is the final step in this process 和 is performed following the st和ard test method ASTM C39/ AASHTO T 22. The prepared concrete test cylinders are placed in a concrete compression machine 和 loaded axially at controlled rates until failure.

Within the context of construction materials testing, 混凝土压缩机器 rank among the highest-capacity loading devices used, 和 their purpose is straightforward. However, there are defining characteristics to look for when choosing a concrete "break machine.”前一个 吉尔松博文 contains helpful information on selecting the right concrete compression machine for your lab.

混凝土抗压测试

Important Steps for 抗压强度 Test Procedure

混凝土 cylinders for compressive strength must be tested while still moist from the curing room or tank. Essential steps for performing the test:

  • Place the cylinder on the bottom platen 和 align it carefully with the compression machine's loading axis.
  • Zero the loading indicator of the compression machine.
  • Manually tilt the spherically seated upper platen to align it with the top surface of the cylinder.
  • 应用负载. If using unbonded caps, check the sample's perpendicularity with a 验证设备 before the load reaches 10% of the anticipated strength.
  • The first half of the total anticipated load can be applied at a higher controlled rate if desired. The latter half of the estimated load must be applied to the specimen at a rate of 0.25 ± 0.0mpa /s[35±7 psi/s].
  • Continue loading the specimen until the load indicator drops off steadily, 钢瓶明显断裂了.
  • Record the maximum load 和 calculate the compressive strength.
  • Describe 和 sketch or photograph the fracture type, as shown in Fig. 1

混凝土圆柱试验裂缝类型

混凝土 Cylinder Fraction Type Key Note

We hope this blog post has helped you underst和 what is involved in making 和 testing concrete test cylinders. Please contact the testing experts at loveBet爱博 with questions about your specific applications.

 关于作者本·巴克斯

Helpful 混凝土 油缸测试 Resources:

试验方法和规范:

ASTM C31 / AASHTO T 23 - Making 和 Curing 混凝土 Test Specimens in the Field

ASTM C192 / AASHTO R 39 - Making 和 Curing 混凝土 Test Specimens in the 实验室

ASTM C470 / AASHTO 205米 - Molds for Forming 混凝土 Test Cylinders Vertically

ASTM C511 / AASHTO 201米 -潮湿养护室 & 养护用储水罐

ASTM C617 / AASHTO T 231 - Capping Cylindrical 混凝土 Specimens

ASTM C 1231 - Unbonded Caps for Cylindrical 混凝土 Specimens

ASTM C39 / AASHTO T 22 - 抗压强度 of Cylindrical 混凝土 Specimens

吉尔松视频:

loveBet爱博 Single-Use 混凝土缸模具

吉尔森全固化混凝土养护箱

混凝土养护设备

loveBet爱博灰色铁9000封顶化合物

吉尔松大熔炉

loveBet爱博 混凝土抗压测试 Machines

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