硅酸盐学报

石膏种类对掺减水剂水泥浆体流动行为的影响

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舒鑫 ¹ , 张倩倩 ¹ , 杨勇 ¹ , 冉千平 ¹^,²

硅酸盐学报 | 化学外加剂助力现代混凝土绿色低碳与高性能化专题—研究论文 2025,53(3): 497-504

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硅酸盐学报 |化学外加剂助力现代混凝土绿色低碳与高性能化专题—研究论文 2025 , 53 (3) : 497 -504

石膏种类对掺减水剂水泥浆体流动行为的影响

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舒鑫¹, 张倩倩¹, 杨勇¹, 冉千平¹^,²

作者信息

^1．江苏苏博特新材料股份有限公司，高性能土木工程材料国家重点实验室，南京 211103

^2．东南大学材料科学与工程学院，南京 211189

通讯作者:

张倩倩（1986—），女，硕士，高级工程师。

作者简介:

舒鑫（1987—），男，博士，教授级高级工程师。

Effect of Gypsum Type on Flowability of Cement Pastes with Superplasticizer

Xin SHU¹, Qianqian ZHANG¹, Yong YANG¹, Qianping RAN¹^,²

Affiliations

^1.State Key Laboratory of High-Performance Civil Engineering Materials, Jiangsu Sobute New materials Co., Ltd., Nanjing 210008, China

^2.School of Materials Science and Engineering, Southeast University, Nanjing 210096, China

Corresponding Author:

ZHANG Qianqian (1986-), female, Master, Senior Engineer．E-mail: zhangqianqian@cnjsjk.cn

SHU Xin (1987-), male, Ph.D., Professor. E-mail: shuxin@cnjsjk.cn

出版时间: 2025-03-20 doi: 10.14062/j.issn.0454-5648.20240608

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摘要

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为探明混凝土拌合早期流动性剧烈变化的本质，从石膏种类出发，采用熟料与不同石膏（二水石膏、半水石膏）制备了5种水泥，聚焦其前1 h浆体流动性经时变化，考察减水剂吸附、矿物相溶解、水化产物析出等过程，从而揭示浆体早期流动性经时变化内在机制。结果表明：矿物相溶解以及水化产物析出、生长是引起浆体早期流动度复杂多样的关键因素。对于二水石膏体系，钙矾石形成导致体系比表面积大幅增加，引起浆体流动度经时损失；对于半水石膏体系，除了钙矾石外，析出的大尺寸二水石膏加速了浆体流动度早期损失，但间隙液中SO₄^2-浓度逐渐降低有利于减水剂吸附，从而导致浆体流动度出现反增长。

关键词

流动性 / 半水石膏 / 铝酸三钙 / 减水剂 / 钙矾石

Abstract

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Introduction

Appropriate workability is a key to ensuring the smooth pouring, building of concrete, and quality of the project. However, in practical applications, the workability of concrete often undergoes unexpected drastic changes in the early mixing stage, such as rapid loss of flowability, false set and so on. The change of flowability of cement paste overtime in the early stage is mainly related to the early hydration of cement and the adsorption behavior of superplasticizer. Cement pastes with different mineral compositions can exhibit different change rules overtime. In the early stage of hydration, especially in the first hour, the hydration reaction of tricalcium aluminate (C₃A) mainly occurs. Since the reaction of C₃A with water is extremely rapid, a large amount of calcium sulfate is incorporated into cement, and gypsum dihydrate (G, CaSO₄·2H₂O) is usually the most important source of calcium sulfate. Although the existing studies focus on the influence of gypsum types on the hydration of C₃A, the fundamental reasons are still need to be explored.

In this paper, the effect of gypsum types was considered to elucidate the fundamental reasons behind the drastic changes in early flowability of fresh concrete. Five cements were prepared using clinker combined with different types of gypsum (i.e., G, gypsum dihydrate and H, hemihydrate gypsum). The study focused on the time-dependent changes in the flowability of pastes within the first hour, and examined the processes such as adsorption of superplasticizer, dissolution of mineral phase and precipitation of hydration products, thus analyzing the intrinsic mechanisms behind the time-dependent changes in flowability.

Methods

Based on the content of C₃A in the clinker, four types of cements with a single gypsum type were prepared via adding G and H, respectively, at two molar ratios of SO₄^2- to C₃A of 0.5 and 1.5, and one type of cement with mixed gypsum was prepared at a molar ratio of SO4^2- to C₃A of 1.5 and a molar ratio of G to H of 2. In the test, the water binder ratio was fixed at 0.3, and the amount of PC was adjusted to achieve the similar initial flowability (i.e., (250 ± 5) mm at 2 min). At 2, 5, 10, 20, 30 and 60 min after adding water, the paste was taken out for various tests (i.e., flow spread, analysis of interstitial liquid, adsorption and hydrated sample preparation).

The flow spread of paste was tested according to the Chinese standard GB/T 8077—2012. The adsorption behavior of PC and the concentrations of [Ca] and [S] in the interstitial liquid were obtained by TOC and inductively coupled plasma mass spectrometry (ICP-MS) on the interstitial liquid obtained by centrifugation. The hydration was stopped with cold isopropyl alcohol (5 ℃) to perform the microscopic analysis on the hydrated sample, including differential scanning calorimetry (DSC) and surface area measurement by BET based on nitrogen adsorption.

Results and discussion

For five groups of cement pastes with the similar initial flowability, the addition of G leads to a rapid loss of flowability in the first 10 min, and increasing the amount of G can reduce the loss of flowability. The addition of H also leads to a rapid loss of flowability in the first 10 min, but then the flowability slowly increases. Moreover, the higher the amount of H added is, the more significant loss of flowability in the first 10 min and the greater the subsequent increase of flowability will be.

For cement with only G added, the precipitation of ettringite mainly occurs in the first hour, and AFt rapidly forms in the first 5 min and then increases slowly. However, for cement with H, two processes occur simultaneously, i.e., ettringite precipitation and H dissolution -G precipitation. H promotes the formation of ettringite, and the ettringite content in the paste is higher than that with only G added.

For cement with only G added, the precipitation of ettringite leads to a large increase in the specific surface area of the system, which in turn causes the loss of paste flowability over time. For cement with H added, the precipitation of ettringite and large-sized G leads to a rapid loss of the early flowability of the paste, but the gradually decreasing sulfate ion concentration in the interstitial liquid is conducive to the adsorption of PC on the surface of the mineral phases, which in turn leads to a reverse increase in the subsequent flowability.

Conclusions

The dissolution of mineral phases and the precipitation/growth of hydration products were key factors causing the drastic changes in early fluidity of the paste. For cement pastes containing dihydrate gypsum, the formation of ettringite led to a significant increase in the specific surface area of the samples, causing a time-dependent loss in fluidity. In contrast, for cement paste containing hemihydrate gypsum, in addition to ettringite, the precipitation of large-sized dihydrate gypsum accelerated the early loss of flowability. However, the gradually decreasing concentration of SO₄^2- was conducive to the adsorption of superplasticizer, thus leading to an increase in flowability of paste.

Key words

flowability / hemihydrate gypsum / tricalcium aluminate / superplasticizer / ettringite

引用本文

舒鑫, 张倩倩, 杨勇, 冉千平. 石膏种类对掺减水剂水泥浆体流动行为的影响. 硅酸盐学报, 2025 , 53 (3) : 497 -504 . DOI: 10.14062/j.issn.0454-5648.20240608

Xin SHU, Qianqian ZHANG, Yong YANG, Qianping RAN. Effect of Gypsum Type on Flowability of Cement Pastes with Superplasticizer[J]. Journal of the Chinese Ceramic Society, 2025 , 53 (3) : 497 -504 . DOI: 10.14062/j.issn.0454-5648.20240608

基金

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国家自然科学基金面上项目(52178215)

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2025年第53卷第3期

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文章信息

doi: 10.14062/j.issn.0454-5648.20240608

接收时间：2024-09-24
首发时间：2026-10-22
出版时间：2025-03-20

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收稿日期：2024-09-24
修回日期：2024-10-18

基金

国家自然科学基金面上项目(52178215)

作者信息

^1．江苏苏博特新材料股份有限公司，高性能土木工程材料国家重点实验室，南京 211103

^2．东南大学材料科学与工程学院，南京 211189

通讯作者:

张倩倩（1986—），女，硕士，高级工程师。

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https://castjournals.cast.org.cn/joweb/gsyxb/CN/10.14062/j.issn.0454-5648.20240608

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2种不同金属材料的力学参数

科 Family	属数 Number of genus	种数 Number of species	占总种数比例 Percentage of total species (%)	属 Genus	种数 Number of species	占总种数比例 Percentage of total species (%)
鹅膏菌科Amanitaceae	2	11	5.26	鹅膏菌属 Amanita	10	4.78
小菇科 Mycenaceae	2	12	5.74	丝盖伞属 Inocybe	5	2.39
多孔菌科 Polyporaceae	8	14	6.70	蜡蘑属 Laccaria	5	2.39
红菇科 Russulaceae	3	23	11.00	小皮伞属 Marasmius	6	2.87
				小菇属 Mycena	11	5.26
				光柄菇属 Pluteus	5	2.39
				红菇属 Russula	17	8.13
				栓菌属 Trametes	5	2.39

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