Sql-server – Why a SQL Server Table takes 1GB more after adding 55MB of data

I've found that one customer database size exploded between yesterday and today.
After investigation I've found a design problem in a table schema but after doing some math I know that 55MB of data have been added to the table but the table size is now 1GB while the original size of the table was 70MB.

For additional information, 55MB of data was added by adding more than 2000 rows with a varchar(max) field filled with the data.

Here is the before/after analysis :

Yesterday

Today

Can you explain to me why a table took 70MB now takes 1GB after adding 55MB of data ?

There is not any index on the varchar(max)

The free space is very low, it is not related to the autogrowth. And the autogrowth is not configured with a percentage but with a fixed growth size.

Here is the creation script of the table :

USE [DuoClient20140003]
GO

/****** Object:  Table [dbo].[tContactHistory]    Script Date: 23/05/2016 10:53:19 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

SET ANSI_PADDING ON
GO

CREATE TABLE [dbo].[tContactHistory](
    [KeyCH] [int] IDENTITY(1,1) NOT NULL,
    [DateCH] [datetime] NULL,
    [KeyType] [int] NULL,
    [KeyF] [int] NULL,
    [KeyI] [int] NULL,
    [KeyCA] [int] NULL,
    [Content] [varchar](max) NULL,
    [KeyCom] [int] NULL,
    [KeyMH] [bigint] NULL,
    [KeyH] [bigint] NULL,
 CONSTRAINT [tContactHistory_PK] PRIMARY KEY CLUSTERED 
(
    [KeyCH] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

GO

SET ANSI_PADDING OFF
GO

ALTER TABLE [dbo].[tContactHistory]  WITH NOCHECK ADD  CONSTRAINT [tAddrCarnet_tContactHistory_FK1] FOREIGN KEY([KeyCA])
REFERENCES [dbo].[tAddrCarnet] ([KeyCA])
GO

ALTER TABLE [dbo].[tContactHistory] CHECK CONSTRAINT [tAddrCarnet_tContactHistory_FK1]
GO

ALTER TABLE [dbo].[tContactHistory]  WITH NOCHECK ADD  CONSTRAINT [tComments_tContactHistory_FK1] FOREIGN KEY([KeyCom])
REFERENCES [dbo].[tComments] ([KeyCom])
GO

ALTER TABLE [dbo].[tContactHistory] CHECK CONSTRAINT [tComments_tContactHistory_FK1]
GO

ALTER TABLE [dbo].[tContactHistory]  WITH NOCHECK ADD  CONSTRAINT [tFoyers_tContactHistory_FK1] FOREIGN KEY([KeyF])
REFERENCES [dbo].[tFoyers] ([KeyF])
GO

ALTER TABLE [dbo].[tContactHistory] CHECK CONSTRAINT [tFoyers_tContactHistory_FK1]
GO

ALTER TABLE [dbo].[tContactHistory]  WITH NOCHECK ADD  CONSTRAINT [tIndivs_tContactHistory_FK1] FOREIGN KEY([KeyI])
REFERENCES [dbo].[tIndivs] ([KeyI])
GO

ALTER TABLE [dbo].[tContactHistory] CHECK CONSTRAINT [tIndivs_tContactHistory_FK1]
GO

ALTER TABLE [dbo].[tContactHistory]  WITH NOCHECK ADD  CONSTRAINT [tMailHistory_tContactHistory] FOREIGN KEY([KeyH])
REFERENCES [dbo].[tMailHistory] ([KeyH])
GO

ALTER TABLE [dbo].[tContactHistory] CHECK CONSTRAINT [tMailHistory_tContactHistory]
GO

ALTER TABLE [dbo].[tContactHistory]  WITH NOCHECK ADD  CONSTRAINT [tModifsHistory_tContactHistory_FK1] FOREIGN KEY([KeyMH])
REFERENCES [dbo].[tModifsHistory] ([KeyMH])
GO

ALTER TABLE [dbo].[tContactHistory] CHECK CONSTRAINT [tModifsHistory_tContactHistory_FK1]
GO

ALTER TABLE [dbo].[tContactHistory]  WITH NOCHECK ADD  CONSTRAINT [tTabShort_tContactHistory_FK1] FOREIGN KEY([KeyType])
REFERENCES [dbo].[tTabShort] ([KeyT])
GO

ALTER TABLE [dbo].[tContactHistory] CHECK CONSTRAINT [tTabShort_tContactHistory_FK1]
GO

ALTER TABLE [dbo].[tContactHistory]  WITH NOCHECK ADD  CONSTRAINT [tContactHistoryKeyI_Chk] CHECK  (([KeyI]>=(1)))
GO

ALTER TABLE [dbo].[tContactHistory] CHECK CONSTRAINT [tContactHistoryKeyI_Chk]
GO