1、 Shape and size of specimen aerated concrete

自上料攪拌車，測(cè)定混凝土立方體試件抗壓強(qiáng)度，也可以按粗骨料大粒徑的尺寸而選用不同試件的尺寸。但是試件尺寸不同、形狀不同，會(huì)影響試件的抗壓強(qiáng)度測(cè)定結(jié)果。因?yàn)榛炷猎嚰趬毫C(jī)上受壓時(shí)，在沿加荷方向發(fā)[本文先發(fā)在礦山機(jī)械/=百///科/=網(wǎng)]生縱向變形的同時(shí)，也按泊松比效應(yīng)產(chǎn)生橫向膨脹。而鋼制壓板的橫向膨脹較混凝土小，因而在壓板與混凝土試件受壓面形成磨擦力，對(duì)試件的橫向膨脹起著約束作用，這種約束作用稱為"環(huán)箍效應(yīng)"。

From the loading mixer, the compressive strength of concrete cube specimens can be measured, and different specimen sizes can also be selected according to the large particle size of coarse aggregate. However, different specimen sizes and shapes will affect the determination results of compressive strength. Because when the concrete specimen is pressed on the press, while the longitudinal deformation occurs along the loading direction [this paper first occurs in mining machinery / = Bai / / Ke / = net], the transverse expansion also occurs according to the Poisson's ratio effect. The transverse expansion of the steel plate is smaller than that of the concrete, so the friction force is formed on the compression surface of the plate and the concrete specimen, which restricts the transverse expansion of the specimen, which is called "hoop effect".

"環(huán)箍效應(yīng)"對(duì)混凝土抗壓強(qiáng)度有提高作用。自上料攪拌車，離壓板越遠(yuǎn)，"環(huán)箍效應(yīng)"小，在距離試件受壓面約0.866α（α為試件邊長(zhǎng)）范圍外這種效應(yīng)消失。

"Hoop effect" can improve the compressive strength of concrete. From the loading mixer, the farther away from the pressing plate, the "hoop effect" is small, about 0.866 from the compression surface of the test piece α （ α This effect disappears outside the range of specimen side length).

混凝土受壓破壞在進(jìn)行強(qiáng)度試驗(yàn)時(shí)，試件尺寸越大，測(cè)得的強(qiáng)度值越低。

In the strength test of concrete compression failure, the larger the specimen size is, the lower the measured strength value is.

原因分析：

Cause analysis:

1、"環(huán)箍效應(yīng)"；

1. "Hoop effect";

2、由于大試件內(nèi)存在的孔隙、裂縫和局部較差等缺陷的機(jī)率大，從而降低了材料的強(qiáng)度。國(guó)家標(biāo)準(zhǔn)GBJ107-87《混凝土強(qiáng)度檢驗(yàn)評(píng)定標(biāo)準(zhǔn)》規(guī)定邊長(zhǎng)為150mm的立方體試件為標(biāo)準(zhǔn)試件。自上料攪拌車，當(dāng)采用非標(biāo)準(zhǔn)尺寸試件時(shí)，應(yīng)將其抗壓強(qiáng)度折算為標(biāo)準(zhǔn)試件抗壓強(qiáng)度。折算系數(shù)需按以下的規(guī)定。

2. Due to the high probability of pores, cracks and local defects in large specimens, the strength of the material is reduced. The national standard GBJ107-87 standard for inspection and evaluation of concrete strength stipulates that the cube specimen with side length of 150mm is the standard specimen. When non-standard size specimens are used for self loading mixer, their compressive strength shall be converted into the compressive strength of standard specimens. The conversion coefficient shall be in accordance with the following provisions.

3、混凝土抗壓強(qiáng)度試塊允許小尺寸表骨料大顆粒直徑（mm）換算系數(shù)試塊尺寸（mm）31.50.95100×100×100（非標(biāo)準(zhǔn)試塊）401.00150×150×150（標(biāo)準(zhǔn)試塊）601.05200×200×200（非標(biāo)準(zhǔn)試塊）

3. Allowable small size of concrete compressive strength test block table aggregate large particle diameter (mm) conversion coefficient test block size (mm) 31.50.95100 × one hundred × 100 (non-standard test block) 401.00150 × one hundred and fifty × 150 (standard test block) 601.05200 × two hundred × 200 (non-standard test block)

二、表面狀態(tài)加氣混凝土

2、 Surface condition aerated concrete

自上料攪拌車，當(dāng)混凝土受壓面非常光滑時(shí)（如有油脂），由于壓板與試件表面的磨擦力減小，使環(huán)箍效應(yīng)減小，試件將出現(xiàn)垂直裂紋而破壞，測(cè)得的混凝土強(qiáng)度值較低。

From the loading mixer, when the concrete compression surface is very smooth (if there is grease), the hoop effect will be reduced due to the reduction of the friction force between the pressing plate and the surface of the specimen, the specimen will be damaged by vertical cracks, and the measured concrete strength value is low.

三、含水程度混凝土試件含水率越高，其強(qiáng)度越低。

3、 The higher the moisture content of concrete specimen, the lower its strength.

四、加荷速度

4、 Loading speed

自上料攪拌車，在進(jìn)行加氣混凝土試件抗壓試驗(yàn)時(shí)，加荷速度過(guò)快，材料裂紋擴(kuò)展的速度慢于荷載增加速度，故測(cè)得的強(qiáng)度值偏高。在進(jìn)行混凝土立方體抗壓強(qiáng)度試驗(yàn)時(shí)，應(yīng)按規(guī)定的加荷速度進(jìn)行。綜上所述，通過(guò)對(duì)混凝土強(qiáng)度影響因素的分析，提高混凝土強(qiáng)度的措施有：采用強(qiáng)度等級(jí)高的水泥；采用低水灰比；采用有害雜質(zhì)少、級(jí)配良好、顆粒適當(dāng)?shù)墓橇虾秃侠淼纳奥?；采用合理的機(jī)械攪拌、振搗工藝；保持合理的養(yǎng)護(hù)溫度和一定的濕度，可能的情況下采用濕熱養(yǎng)護(hù)；摻入合適的混凝土外加劑和摻合料。

During the compression test of aerated concrete specimen by self loading mixer, the loading speed is too fast, and the crack propagation speed of material is slower than the load increase speed, so the measured strength value is high. During the concrete cube compressive strength test, it shall be carried out according to the specified loading speed. To sum up, through the analysis of the influencing factors of concrete strength, the measures to improve concrete strength include: using cement with high strength grade; Adopt low water cement ratio; Adopt aggregates with less harmful impurities, good grading, appropriate particles and reasonable sand ratio; Adopt reasonable mechanical mixing and vibration technology; Maintain reasonable curing temperature and certain humidity, and adopt damp heat curing when possible; Add appropriate concrete admixtures and admixtures.